I'm sure most of these have been suggested previously, but here it goes:
1. Group a selection of tracks to route to the analog filter instead of just one track if possible.
2. Trigger frequency - trigger a sample every 8 bars instead of 4, for example, to play samples longer than 4 bars.
3. File handling of samples within the SP-16 user interface (Delete/Move).
Some "Nice Haves":
1. Trigger copy per step. (Copy/Paste a bar is good enough 95% of the time however)
2. Program Change Send for pattern/scene changes. (Maybe it does this, but I cannot get it to work)
3. Arrangement loop - when configuring an arrangment, have the option to loop back to the first step in arrangement.
1. The analog filter and the great sound.
2. Easy to use interface and very little menu diving.
3. Half, Full, Parameter triggers and parameter locks.
4. Sampling capabilities.
5. Multi outs.
All in all, I really do like the SP-16 a lot. The DSI filter is what separates it from the competition and really boosts its sound. The original price point was too high for what it could do, but DSI components are high end, so I can somewhat understand. But the current price $899-$999 is where it should be for it's capability. Some crucial sequencer and routing enhancements could justify a $1100+ price tag. For an MKII, it would be cool to have a cross fader or be able to use the slider as a cross fader between choke groups for example.