Probably possible with some scripting, I came up with this Lua script real quick,, I really don't know reaper/lua very well but seems to work OK.
Code:
-- Activate next MIDI track and arm for record.
editor = reaper.MIDIEditor_GetActive()
reaper.MIDIEditor_OnCommand(editor, 40835) --< Activate next MIDI track (40835)
-- reaper.MIDIEditor_OnCommand(editor, 40836) --< Activate previous MIDI track (40836)
take = reaper.MIDIEditor_GetTake(editor)
track = reaper.GetMediaItemTake_Track(take)
reaper.SetMediaTrackInfo_Value(track, "I_RECARM", 1 ) -- 0=not record armed, 1=record armed
EDIT Take that back, doesn't really work the way I was expecting.