Renting heroes

So…I know that to get the heroes I want and to ascend them, I’d need to build up an overdraft the size of a small country’s (say, post-Brexit UK) national debt. So I don’t pay to summon any more, ever.
But why not let us rent a hero. I’d do that, maybe 1000 gems for a month / week. Possibly restricted so you can’t use in defence.
Anyway, need something to bring back the interest. Game’s a bit tedious at the moment.