The 1st thing I would suggest is that sonar learns to better adapt. Right from the get go sonar is a right royal pain in the butt. It fails to optimise itself for the hardware it is being used on. We have to learn how to adjust our midi buffers.. How many AAA software games expect the end user to know what to set the graphics for there hardware ? Sure some of us know, but it attempts a half decent job by itself. So why is sonar expecting the end user to learn the intricacies of it's preferences ? Especially when these setting are so important to the quality of the sonar experience.
The second would be stability, Sonar is unstable, especailly if you haven't optimised the programme for the hardware you are using. It also is far too reliant on well written drivers. Here we have a majority of computers with windows running on board sound-cards and Sonar behaves awfully with all of the ones I have used. Even after that hurdle of fixing that with a new sound card Sonar is unstable. Not to the point of making it unusable, but enough to make my eye's roll on a near daily occurrence. I get many issues with Sonar crashing to desktop, some due to VST's some not. Example changing the colour on the track view with Ctrl held to change multiple tracks causes a CTD.
Third, It is missing recognition, sure the industry have heard of cakewalk, but enough to mention it in there list of suggested DAW's for the use of there £200 software VST, or there £4k control surface ? Sonar is IMO very professional software, yet it is probably looked at like a hobbyist 50 year old rockers DAW of choice. It's ageing flagship VST's don't do it any favours, Square I, Roland Groove Synth, Cakewalk TTS-1 and even Z3ta are really showing there age. I love Z3ta, but it's 2017, and my resolution is now 1920 x 1080, I can't even read the damn thing to programme it on my 24 inch screens.
Forth, Sonars step sequencer.. This is in sour need of updating. Why can it not handle poly rhythms like Geist 2 can ? Why can't it create tempo's unique to the step in the step sequence like BreakTweaker micro edit can ? Vital bits I find is essential in creating NEW sounds people haven't heard before. Now if you can get that down, you open that up to EVERY single VST that understands midi notes that sonar can host. Sonar might even start losing some of the ageing rocker image it has, well at least to my mind.
Five, I have loved the way I can BPM sync some of my effects, and filters in a fair few of my VST's soft-synths (Serum for example or Massive). I love how I can create Poly rhythmic patterns in Giest 2 or in Xfer's Nerve, I love how these soft-synths can also use step sequencers to control all the wonderful parameters. Now what is stopping sonar creating a way to make these methods to control any VST automation ? A more modular approach to automation. Just imagine a drop down list to assign a control (BPM Sync's ADSR or LFO / LFO / Step Sequencer) to a type of automated control for a soft synth or effect., instead of having to draw manually, or set up a midi device via midi learn / ACT record, tweak knob, playback. There's nothing wrong with either of those two methods, much.. but what you are effectively doing is taking a fantastic innovative feature, and making it apply to every single VST you own (synth's + effects) ?! seems a no brainer to me not to have this.
Six, A good emulator for the classic 909 / 808 would be a huge step forward too.
Seven, I like to see a much better Arp more akin to xfer's Cthulu.
Hope that helps ;)