Concept SUMMONER SPELL: BUTTRESS Bonus scaling Armor and MR multiplyer

Figure I would repost in the concepts boards. It is probably more appropriate. People don't seem to respond to new ideas with a lot of vigor. It can be hit or miss with getting feedback on these concepts.

SUMMONER SPELL: BUTTRESS Would you pick a spell that got better as the game progressed instead of what most Summoner spells seem to do? Buttress would reduce your mobility for a few seconds but Increase any ARMOR or MAGIC RESIST you had built. It does not give armor or resist if you haven't built it so it wouldn't take the place of Barrier. And it keeps Tanks from getting too juggernautish early on but really helps on engagements later game.

The balance would have to be played with in PBE but lets just start with: **30% MR and Armor from any bonus MR and Armor built, Duration: 4 seconds, cooldown: 210, Size increase 12%, Move speed reduction 15%, Tremor foot stomp sfx **

It was brought to my attention that Galio, Rammus, Malphite, and Taric might get additional bonuses from this if not coded out excluding their buffs directly. How do you feel about this? Would it make them too beast mode or is it icing on the cake?