For now cheap China edge connector selection seems to be favoring old .156 spaced ones.
Couple years forward and situation can be totally different.
But if old TM500/5000 Series plug-in interface is enough then why not.
Just buy as many connectors as you think you can use, now and ever.
Double row header connectors are also available and most likely remain so.
Their long time problem is connectivity.
But you can always do a yearly maintenance day and scrape the surfaces.
Back in the day when computers had many sockets their connections were real problems.
Even more when every chip were socketed and qualities were not great.
That is definitely a thing you don't want.
Another problem with headers is power, they are really not for that.
And if you want to keep some pin naming standard of something that has a single power pin, pick another connector type.
You can of course combine bigger connectors to the construction but that is not going to help with bad connectivity of a header.
Ready made fingerboards seems to be a bit out dated and so expensive.
On top of this page is a solution, I've heard.
Maybe few new skills are needed but so, people can learn.
Generally my prediction is that the situation will geatly ease up in the future.
3d-printing will do all plastic guides and holders, if they are not already.
And aluminium plate milling and printing has been a regular thing for years.
Bar profiles are easier, you just need few and cutting in the work shop is trivial.
Problem with bars can be that supplier has only full ones, that's 6m here.
Nuts and bolts here are scaled hardware store stuff, they also have small screws, so Rittal is not needed.
Only thing still missing, or at least for me, is a concentrate of online shops of those.