Litter on the Op side all you will need to do to build around this is unupped fire queens friefly= light emitting creature=lots of them. It will be way easier then trying ray of lights cause you can just keep making fireflys
You lose out significantly on offence. No matter how much damage reduction on Hope, you can't kill Fire Queen if she has a whole field of FireFlies out, while she can one hit you with a Fire Lance. Although technically you really only need 3 LightFlies out against Fire Queen, it shows how too much defence could effectively kill you if you can't balance the offence that is coming in and going out.
Gemini, Graviton and Obliterator, all 3 using "Unstoppable" momentum cards, will put a serious dent in your "Hope" shield. This is coupled with the fact that it is not very easy to Creature Control some of these Gods without drawing a specific set of cards (Eternity + PA, Eagle's Eyes + PA + Quint + Oty, Quint+Oty+Fire Storm, etc) and in the process of waiting out for a means to destroy these sources of damage, you could seriously suffer. Of course, the same fate may await those who use other methods of stalling, but seriously, a Phase Shield would work out better here.
ATM, I think people are overestimating the effectiveness of the card. There are so many ways to counter it, and the same ways to counter Hope are the same ways to counter Phase Shields, Sundials and whatnot. A quinted, momentum Fire Spirit would wreak havoc. In most standard rainbows, 2 FFQ for lightflies is redundant.
Only a niche deck will be able to capitalise on the effects of Hope, and using these niche decks poses a new set of problems.