As for "popular in the future", brass will always be available for the .25-06, .270 Win, so necking up or down should not be an issue.
Powders are getting revised and added to all the time, and with the slower burning powders coming around, a longer barrel is more acceptable to gain velocity.
Primers have not changed much in the past years, and I see no foreseeable change either.
Bullets are changing for the better all the time, and with the 6.5/.264 market growing like it is with the long range game and hunters, I see the popularity sticking around for a long time too, especially in the higher end bullets like Berger, Barnes, Hornady, Sierra, etc. Used to be only a very few factory .264 offerings like the .264 Win Mag (another candidate to consider!) and the 6.5 Rem Mag (now pretty much obsolete except hand loading and custom chambering).
Once you buy a quality set of dies for reloading, you should be set for life with them, so no need to replace there either.
I see the 6.5-06 being a very easy candidate for long range hunting, and even for women/kids to shoot as well. My .25-06 Ack. Imp. is easily shootable by my 10 year old daughter, and she even shoots the .270 Win with a muzzle brake. You could always add one of those and really get the recoil down to tolerable levels.
Whatever you do, get a quality built rifle, good optics, and work up a good handload and you will be set for a long range medium game rig. Antelope, deer, etc. will not know what hit them. My neighbor has a .264 Win Mag and he has shot Coues whitetail between 600-980 yds. every year in Mexico, usually more than one a trip. Makes me so jealous......