...This means that if Dash owes someone money in the future, because we signed a contract in Dash, we have to pay it, at the cost of what those funds could have otherwise done for us.
We can't see the future.
Tante -
I don't know if you realise it but you just fired the starting gun on demand for a Dash derivatives market. The way companies usually address this risk in "the real world" is by means of hedging derivatives such as futures contracts or currency swaps.
Maybe the blockchain could purchase dollar futures contracts and hold these for the purpose of allocating long term funds. Those contracts would hedge the fund against fluctuations in the Dash exchange rate while at the same time supporting successful applicants with predictable budgets.
(That's what a financial derivative is supposed to do when it's not busy blowing up the world economy).