As the post name suggests - I have some suggestions for the mixer, some of which have been requested before I know, but here we go -
MOUSEWHEEL SCROLLING -
Mousewheel scrolling in the mixer currently has some issues. If you are adjusting a fader with mousewheel scroll and your positioning isn't bang on then the mixer will fly (at a rate of half a page per nudge!) in one direction or the other, not only have you lost your place but you often end up centred over a different track and adjusting that tracks volume fader instead... not ideal. I would like a preferences option to completely disable the horizontal mouse wheel scrolling in the mixer, except when the mouse cursor is hovered over the grabby bar at the bottom of the mixer. Another solution would be an option to assign mousewheel mixer scrolling so that it only works with a modifier.
It would also be nice to have a 'smooth scrolling' option that only travels one track per click, I understand that this may not equate to exactly one track per click on every mouse on every OS, but they would all be noticeably smoother at least. Edgemeal made an excellent script for this for me (thank you!). It's awesome and I use it constantly now, but it can't override the main mousewheel action, so it doesn't solve the issue above. However, we know it's possible now, so hopefully the Devs will consider a native implementation.
When the mixer auto-scrolls to a selected track, that track either ends up at the far left or far right of the mixer (depending on whether it was above or below the previously selected track). It would be much more helpful if the mixer centred itself on the selected track when auto-scrolling, so you know exactly where to look. Currently you have to try and scan opposite ends of the mixer to see where the selected track is.
TRACK SELECTION/IDENTIFICATION -
If you have the preferences option 'mouse click on volume/pan faders changes track selection' and you shift-click to bypass a plugin in the mixer that is on a different track than the currently selected one, it selects ALL tracks in between the two. The plugin bypass action should override the multiple track selection in this instance.
It would be nice if we had a native option to make the selected track in the mixer VERY obvious - like a big white border around the whole mixer channel. I know you can get close to this if you are a theming wizard, but most of us aren't, so a native option that works regardless of theme would be great.
I'd also like to see clearer differentiation of parent AND child tracks in the mixer. Some of these have been partially done in the new Reaper 6 theme, but I'm not a fan of that theme personally, so I'm hoping that we can get some preferences/theme tweaker options that would allow us to implement some of these new options in older themes (like the child track indenting in the mixer). We've got that lovely little routing box with indication for master/parent send, other sends, and receives. I would love to see a similar indicator for child or parent status... in fact I'd find that much more useful than the send indicator. It's always clear when a track has a send by looking at the mixer, because if you're using sends, then you are probably also displaying them - it would have been more useful to use that space to show child/parent status IMO (not going to get changed now I know, but perhaps there something else that can be done).
FX -
A 'replace FX' option when right clicking on FX in the mixer would be great.
A copy/paste FX settings function would also be great. Obviously it would only work when copying and pasting settings from the same plugin.
The option to colour VSTi's differently from the standard FX in the mixer would be really helpful. Doppelgangers excellent FX list script is able to do this (I believe just by using the 'VSTi' prefix as a cue for the colour change) so I see no reason Reaper can't implement it natively. Doppelgangers script also provides a different colour for JSFX, which would also be nice.
A graphical prompt when dragging/dropping FX would be helpful... whenever I drag and drop FX in the mixer it's always slightly unnerving that I don't know if I've grabbed the correct one until I've dropped it, or even if I've missed and just grabbed nothing. The usual method from other DAW's is a translucent version of the FX 'box' from the mixer, that moves with your cursor while dragging.
EMBEDDED PLUGIN UI'S (only in the RC release at the moment) -
Some probably see this as a bit of a novelty feature - but the ability to see all of your EQ settings and frequency response for every channel at a glance REALLY is a massive workflow boon. However, it's most effective if they are all neatly lined up along the mixer, so you can instantly see if you've missed a HPF or LPF on a specific track, or quickly spot where conflicting frequencies might arise across many different tracks at once.
I'd like to see a separate, optional, resizeable section in the mixer with it's own 'handles' just like the FX controls section, that could hold the plugin UI's.
Bear in mind, Justin has said once the dust has settled on this new feature he will release the API so people can make these mini mixer UI's for third party plugins - I believe this will be an absolute game changer for many users, I know of no other DAW that has a feature anywhere close to this that works with third party plugins. Someone could make a bunch of these UI's for the most used plugins - Fabfilter/Soundtoys/Valhalla etc... and charge a fee if they wanted. If they're functional and looked half decent then I think they'd make a killing.
FULL TRACK PARAMETER LINKING -
Reaper links certain parameters of selected tracks already which is great. It would be nice if we could link ALL of them. We have some excellent live FX parameter linking scripts, but if we had this fully implemented natively then we could also link send controls, and link the adding/removal of plugins and sends. It would work by slot - so if you adjust/remove/add a send or effect in a certain slot then the same happens on the respective slots across all selected tracks (while this linking option is turned on of course).
POST FADER FX - self explanatory and already much requested, but worth mentioning.
Apologies for the long post, I thought it was better to just put all these thoughts in one place rather than flood the forum with individual mixer FR's!
I can provide gifs/more explanation for any of these requests if needed. I didn't bother as this post is long enough already