What's this? Inno is asking our opinion before making a major change to the game? Do my eyes deceive me? Was that a flock of flying pigs I just saw swooping through my city? An unexpected development, but definitely not an unwelcome one.
In terms of ratios, I am generally quite happy to accept tier3:tier2 or tier2:tier1 at a ratio of 1:2.5 or better, e.g. 1000 elixir for 2500 crystal, and 2 tier difference at a ratio of 1:5 or better, e.g 1000 elixir for 5000 marble. I appreciate that the maths can be a bit tricky for this though, and some nice round numbers are preferred.
I'd say the proposed ratio of 1:2 for tier3:tier2 or tier2:tier1, and 1:4 for tier3:tier1 is an acceptable balance. The alternative of 1:1.5 seems quite generous, and makes the maths a little more tricky, so I wouldn't recommend it.