One reason I own 270, 308, 223, 30-06 and such is that I know ammo will be around for a long time and be inexpensive. I don't fault the rifle companies needing to make new things to keep their profits going, but yeah many new cartridges are going to be gone or dying in 10 years. It's just the way the game has always been.
I own a 6.5 Creedmoor as of this year and the Hornady factory ammo is moving at a blistering 2553 fps. Anemic as crap, but at least I have that high BC as I watch it underperform the 270 in basically every single metric. However, I'm shooting a modern cartridge design and I'm told by very important people this is an improvement.
As for making a fast twist 270, I don't see any reason why it wouldn't work and stabilize the longer bullets. The same way they have made 223 loads for 1:8 twist with heavies for those twist rates. If your slower twist doesn't stabilize them, oh well. Try another load.
People compare the old vs. modern cartridge design and think they've hit on some deep and insightful point. But the reality is that the older cartridges were built for an entirely different purpose (war and reliable feeding with tapered cases and looser chambers vs. target (straight wall, fast twist, and match chambers). Certainly the magic of straight wall cases, sharp shoulders, fast twists, and match chamber tolerances were not above the understanding of the older designers. They just chose to not use them for their application.
There's not any more magic to it than the above. Shooters have to use what's important to them and what they enjoy.
If you want the higher potential accuracy of the modern designs, you need to keep them cleaner and expect shorter barrel life. You also may not find factory loadings for them in 10 or so years. Just buy a new barrel and re-chamber to the latest belle of the ball.
If you want more room for feeding reliability in the field, and are not trying to shoot 1,000 yards on the regular, the older designs are very well proven and common as dirt so you can always shoot them.