Check the contract / terms regarding stair-casing and selling very carefully. We bought a shared ownership in 2007 and it promptly fell in value when the market crashed. I think this is worth knowing and checking as we are potentially looking at house price falls this year.
We owned a 35% share and understood that as the value had fallen we would either have to ride it out or lose money. After 4 years we were keen to sell. We had paid down the mortgage and had some savings so were prepared to take a loss on the fall in value but found if we sold we had to pay the shared ownership company 65% of the higher of the market value or original price.
So then we thought maybe we can staircase and at least we will own more but again the staircase terms were calculated using the higher of market value or original price.
Basically in every situation the shared ownership company enjoyed the upside but we took on all of the downside and had to pay them for any fall in market value. Not all are line this so it really is worth checking.
We sold as soon as market value came back to what we had originally paid. I know you said you're not looking to move but you never know how circumstances will change.
In terms of selling we had always been told that we could only sell our share to a three shared ownership buyers and that massively restricted the pool of buyers- we advertised it for ages through the shared ownership company with not a single viewing.
I honestly thought I would be stuck in that little flat for ever but luckily we found out that a neighbour also on shared ownership had marketed the property full price on the open market and their solicitors did a 100% staircase and sale simultaneously and we did the same.