Any chance that all raids could become relevant in some capacity in the future?

[Vidu]

I think it would be beneficial still, because it would add in a variety. I currently run my alpha raids weekly to get the rewards, but aside from that there is no incentive for me to raid any further. And after however long, eventually running four bosses gets a tad stale. Mix in a legacy raid here and there to spice things up, and it'll become a lot less repetitive.

YOU can mix in other content if you want to play other content.

For Savage raids your main motivation "should" be wanting to see and learn a cool new fight - not gear (its a legit reason to raid though, obviously).
And you wont be able to do Coil and Alexander Savage like you're doing Alpha NM, let me assure you of that...