The whole Ti bike for life thing is so unlikely to be realised. If you’ve spent that much on something high end, eventually you’re going to want something more current, and that’s assuming it hasn’t broken or become too outdated to find components.
I’ve had a few ti bikes and I’d agree with that. But there are ti (or any other material) bikes that are either unique enough to be real keepers, or just bikes that ride well for you and just don’t need updating – a good road bike with 1 1/8 front end, threaded BB and reasonable angles, maybe enough room for 28C or a set of slim guards at a sqeeze, etc. Very few MTBs make the keeper-list for me but road/tour types can quite often.
If I had a few grand for a custom now it’d be steel, no question. More choice in tubes, builders and detail than Ti. More durable and more potential to replace tubes if it’s brazed. Ride quality is comparable, better in some ways but a little bit heavier. Not much though when you look at ti frames that aren’t noodles. A real ‘bike for life’ is rarely if ever an all-out performance bike, more of a cover-a-few-bases job, so a bit of weight shouldn’t really be an issue anyway.