I seen goals on sales. But I do not recall those goals to be there for any specific actual goal. Never understood the purpose of those.
Why should you not be allowed to make promises? Just make no promises based on inciting users to do things against the tos. Like giving fake votes.
I think you can sell a set of limited things. Never really understood those, but your donation goal would be reached, if all those "items" were sold.
But this has the disadvantage, that you might add those features regardless or with less donations and then are in a bind to either not release it, or make the donation goal obsolete, breaking your promise.
Maybe be unspecific and just encourage people and be vague that you might implement certain features if players are generous and interested, so you do not need to backtrack, should not enough donations come in.