If heat.gg is not making a provably fair one (they literally stated themselves) then there is no point on playing there, it all comes down to trusting the website and why would I, I wouldn't mind playing there with provably fair games, I have nothing against anyone in the crypto world but if it is not provably fair then I am not going to really risk it.
Also, you are definitely right if there was a way to provide hash myself I wouldn't play there neither because it is way too much work to put for just a simple RPS game, if there is a way to make RPS provably fair without too much work (basically just clicking) then I would love to play there, if there is nothing well I am not playing RPS right now so I would just continue to do that until someone figures it out.
I'd rather refrain from advertising the site on devans thread, however we do have two other modes (Jackpot & Coinflip) Which are 100% Provably fair with unmined hashes from EOS blocks determining the winner.
There's a lot of complications when designing a provably fair system for RPS that's both user friendly and safe.
Like I said above, there's a way to do it however it introduces a huge window for user error and user experience is thrown out, as well as the additional learning curve of the play-style.
You can make RPS provably fair if it were house based i.e house creates games, however I feel this also takes away the unique feel of it as RPS traditionally is more known for not being a game of complete sheer randomness, and there's some minor strategies you can employ such as getting in your opponents head, conversely you could just randomly generate your choice.
Playing against the house basically just turns it into any other dice game / coinflip, where the outcome is you either double your money, draw, or break even.