If they got rid of stupid memory cards I think vita could reach 20 mil easily

I highly doubt it, but that would make me sell my OLED model and buy the new one immediatily.

Edit: Unless they figured out some kind of adapter for the older models.

If they did resolve the memory card issue and a price cut I'd seriously consider buying a back up Vita.

It doesn't need a redesign, it needs games...

Any chance? yeah...
Will happen? probabily no.

I hope so and it should be an actual upgrade unlike the 2000:

-Slide up design like the PSPGo
-Slightly wider analouge sticks
-L2/R2 buttons for remote play and PS now
-32GB internal memory. Japanese Vita games aren't big enough to really need more then 32GB so this should resolve the memory card issue.
-Better screen (at least LED)
-7-10hour battery life.
-HD camera

Sell the new Vita for a minor premium over current prices and cut the price of Vita 2000. 

I dont Sony would bother wasting the money needed to make a new model UNLESS they can recall old units and refurbish them as newer models are a drastically reduced cost price.
So my answer will be no, unless you count different colours as new models.

If they did release a new model? Well it wouldnt help sales much more than a month or two of boosts.

Not impossible, as PSV computing power is comparable to current mid-low end smartphones and the screen is good quality but mid resolution, anyway a major redesign won't come until the current model will have reached sales high enough, and anyway they can wait some more time, until late Autumn to launch, when a new model will produce a higher boost, with the additional benefit for stores to be able to get rid of old supplies using them for BF special offers, so catering not only for richer buyers with the new models and bundles but also for the less rich ones.
Instead of expensive and slightly less durable OLED, they could use Quantum Dot LED for the screen, to bring higher quality at reasonable cost.
A launch at the beginning of Xmas season would maximise the return from marketing costs, making them more justifiable to shareholders, moreover they could use the surely larger marketing funds for PS4 to benefit PSV too mentioning Cross Buy, Remote Play and other PS4-PSV synergy features whenever appropriate. If the base PSV model will be cheap enough, high-end PS4-PSV bundles could be priced a lot more attractively..
PSV sales are low and even a good boost won't make them become stellar, so Sony will have to carefully choose the launch period to maximise the return of marketing and new model production starting costs, as with sales that in the rosiest case will be in the very few tens million sales (if the new model will allow PSV to reach, say 25M in the worst and 40M lifetime sales in the best case, compared to 20M at most if they barely keep the current model afloat until its natural death with two price cuts, one this year and another a couple of years before retirement, and a few big games every now and them), even a few hundreds thousand sales more or less could make the difference between a good and a bad investment.

I don't think changing memory cards to SD/micro would be the best solution incase current Vita owners would want to upgrade their Vita but will now need a different memory card.

The better solution is to just make the priority Vita memory cards the same price as SD cards. Price really seems to be the main issue for the memory card moreso then the actual type of memory card I believe.

PSP Go was the best system created, so if they can make a new Vita similar is design and features that would have me sold.

The price shuld go down