You can play it on multiple tracks, but you won’t hear it on multiple tracks. Same as with plugin based instruments.
I’d love to remove this constraint too, but it’s - well - complicated, up to impossible, not worth the downsides, or should be done completely different.
Seehttps://forum.renoise.com/t/done-3-1-instruments-with-fx-are-tied-to-one-track/40268(Old 3.0 beta discussion about this)What we have now in 3.1 actually is the result of the last beta’s discussion.
Not sure what you mean, I put three notes on three different tracks, and played it. All track VU meters showed activity. Also, when adding an external FX (e.g. filter), on the third track, only the note played on the third track was affected by that effect. The instrument behaved exactly like an instrument that does not have any internal FX at all.
When I did the same in 3.0, then only one VU meter showed activity, as the audio was routed to one track only. But in the current beta I do not see this behaviour.
So either I just discovered a very obscure bug, or I am totally missing the point of what you are trying to explain 
EDIT: Check the attached example. Three notes are played on Track 1, Track 2 and Track 3, respectively. All three notes are routed to FX chains that include a LofiMat and are routed to ‘current track’. I added a gainer with -18dB to Track 2. Play it and watch the mixer to observe that (1) all VU meters are active and (2) the gainer only affects Track 2.