The balance is a non-issue. What you describe has already been invented previously, and nobody bought them.
Google for "stabilizer sup"... goo.gl/UxZebG
Just get a stable enough board.

Think of learning to ride a bike. Yes stability is an issue for the first minutes, but side wheels already exist, there is no market niche for innovative side wheels.

If you want to innovate, I guess you should concentrate on solving issues for regular SUP riders, not just during the first learning hours.
People already addicted to SUP will also be more keen to spend money than beginners. E.g you just bought something on Amazon, I guess because it was cheaper than buying locally from a shop who would had advised you on the proper board width for your body size/abilities.

Some ideas:
A leash you do not step on and that does no drag in the water?
Holders for spare paddles for downwinders?
A safety system to be able to paddle back to shore on an inflatable if it gets pierced?
Something to ease cruising around with chidren (or dogs?) on the board?
...

I want a board that changes width while I am in the surf.

Imagine having a shorter board that would be great for surf, but with side wings that pop out when you are paddling back out or standing out the back. The side wings provide stability, but they would slot back into the board, based on foot pressure, when you paddle for the wave and catch it.

It would be better if the side wings slotted away based on telepathy, but foot pressure is OK for version 1.0.

Ok thank you all for the feedback! Good to know I've been looking in the wrong place for improvements so I can start looking in the right place. You guys really are helping me out a lot with just a couple seconds of your time with a comment, so thanks again!

I went to a local SUP shop yesterday and they also said the stabilisers weren't that necessary, and said its simply a case of buying a bigger/correct board for my size - makes sense!

I've added about 40 SUP clubs/groups on Facebook and received a couple comments from regular suppers to shop owners which were all positive. a lot suggested the focus on beginners.. but Colas you're right, after 10 minutes on a bike you no longer need the stabilisers, so why would you need these for longer? *Just a thought, I've been on some really calm rivers and my balance has been great on the inflatable SUP I have - no issues at all. but when I transitioned to the open sea the other day it was a different experience altogether - I spent almost 40 minutes just focusing on balance which really killed the joy for me, and I was just so tired because of it. -The shop suggested purchasing a bigger and 'better' board - which, makes sense - but their kit was ?700-2k - as a student on a budget, I'm not really looking to spend over 300/400 on a board for some fun - just wondering whether theres more people out there who are similar, who can't simply afford to buy better stuff who still want to get in on the fun - potential market??

Additionally, I'm just wondering whether there could be some kind of stabiliser aid for choppier water that extends out (very similar to what cantSUP enough/VIC said) - and when you're on still water they're basically no existential. -So the user could control them entirely? That way they're not in your way when you don't want them, and they're there when you need them.

In relation to Tardys comment, I've also had a lot of feedback in relation to doing something for fishing SUPs! Potential areas including a chair/storage space that is super lightweight and comfy and desirable looking (not just your regular fishing box which I've seen used a lot), - instead something really quite sexy and potentially modular that could transform shape into maybe a kneeling mat or lying down mat? Potential to put all your fishing gear in it, food, drink etc with built in rod holders? Does anyone think this is a good idea?

Also had some more comments in relation to stabilisers for fishing - suggesting that when paddling out they're not needed - but when you've found your spot you extend these floats out and you can forget about needing to balance because they're doing the job for you - with potential to put your gear in these floaty pontoons too?

I really appreciate all the comments, negative and positive, - I really wanna do a 10 week project on SUPs, but if I can't find a good enough area that all you guys think is worthwhile ill have to change topic entirely (and be very sad)

-Mike

Hi Mike ...maybe look into a inflatable dugout SUP for fishing ,just width in a board will give stability ..and if you are low in the water eg. sitting
the extra pontoon or outrigger may not be necessary.maybe a extra fin will give this ,like a mini centre board .or one each side as a stabiliser ,which can be pulled up for paddling .OR large twin fins.
I'M guessing this is a project .?

Hi mike - ive emailed you some info on a concept - let me know what you think