Hi Michael.

@You : "So it's fairly likely that improvements will come not from working on it myself but from licensing it from some other company."

I agree with you.
Improving Filleting and Shelling (and offsetting) area it's a HUGE, HUGE task that it's almost impossible to be achieved by one person company.
The only feasible thing is to buy a license to integrate some robust and fast kernel developed by some specialized company (KCM or other)

@You : "I had previously planned on licensing one for that purpose but it doesn't look like it will be ready for the v4 timeframe unfortunately."

I think that your main problem now is that it looks like you're a little too late about that.

2016 is over and also 2017 is going by so fast.

I hope I'm wrong with my remarks because Moi 3D deserves to stay at top places of nurbs modelers for artists.

IMHO the main lacks of MOI 3D are :

1) 64 Bit 2) Instancing 3) Grouping 4) robust Filleting and Shelling

If the point 1 it's almost ready I fear that the points 2 3 and 4 aren't.

Michael, I sincerely hope that you will find enough energy, for example with some external help, to add those features as soon as possible.

Moi still has a great advantage over it's main competitors, that is its "STATE OF THE ART" workflow and UI,
but you HAVE TO RUN AS FAST AS YOU CAN because the last 3 points I've mentioned earlier are too important to be omitted.

I wish you the best and I stay tuned!

Marco (mkdm)