Sounds interesting. I like the idea of a revenge window, but if you get online raided your probably unable to exact revenge that day lol. When the raiding players are at your base, their base will be unshielded, so if your large enough you could send a breach force while you have some blocker/defenders, and that is as proposed. So revenge windows should be looked at but after we see how the game starts to take shape after this.
This may enable longer inter-wipe periods, and allow trade to develop and discourage the "quit until next wipe" mentality that hurts this great game.
It may require alot of balancing, but you have a lot of balance points to tweak.
I also propose , down the pipe, but keep in mind when designing this shield if you like it ,some sort of "capital" shield that enables safe trade within an area, nullifys weapons, but allows randos to move in and out for commerce. Maybe this costs prag to maintain, maybe they have to maintain a close base that is always vulnerable, like the start wars death star shield.
Your right a change like this alone could allow the emergent patterns to start to open up more.