Dear OP,
It doesn't work that way. You've made a purchase because (hopefully) you want the things you've bought. That money has gone into the Frontier bank account. Once it's there it's up to Frontier to do with it what it wants. Spend it on new IP, new development or enhancing Development of Elite (in addition to share holders, taxes, etc.)
What's probably happened is Elite would have been already set a budget for 2018 and the development would be paid out of that budget, (considering that we're getting Beyond for free, I think the cosmetic purchases must be going quite well). But it would be daft for a company just to have only one or two product lines. It puts the company at risk because if something happens to that product, then the company goes under. Look at what happened to the Marvel Heroes MMO and what would happen to CCP if EVE went under.
Some people are not happy with the development pace of the game, well a decent update once every six months is not too bad (IMHO) and I prefer the approach that's been happening to what's happening over at CIS. I've come to the conclusion that atmospheric landings is not going to be seen till 2019 and Space Legs beyond that (even though I would be quite happy with just walking down to a space bar and chatting with other avatars).