Evo shields in their current form are almost always useless; because you can only pick them up as whites it leaves no incentive to pick them up past the first five minutes or less. I don't believe they're beyond redemption though, so here is some ideas I have had for a while to improve them.
1 Start everyone off with an Evo Shield with or without the shield bar.
2 Count people's damage numbers before picking up an Evo Shield. For example: if you have done enough damage to get a purple Evo then when you pick up a white one it should automatically change to purple etc
3 Another option would be to get rid of every non Evo Shield, apart from Gold, then make both blue & purple evos; if this was done however I would recommend Evos having the same amount of shield bars as their non Evo counterparts.
You could also use ideas from a couple of the above options to improve the usability of Evos. It's really satisfying to get rewarded for doing damage, but in their current form Evos are just not worth using. Furthermore I almost never see anyone with an upgraded Evo, because people rightfully don't want to sacrifice shields. I like the idea of the red Evo because not everyone can get a gold body, but it's just impractical to get currently.