.30-06 isn't obsolete and works fine. It is fairly poorly designed by modern standards, but then again there was a lot we didn't know about interior ballistics back then. If done over, it would be shorter, with a steeper blown out shoulder and higher MAP. Coincidentally, that's what the .308 is.
Higher MAP, perhaps. Shorter and fatter with a steeper shoulder, not necessarily. In fact, it could end up pretty much as it is now. It is interesting that the "poorly designed".30-06 is one of the most used cartridge cases for necking up and down. The .25-06, 6.5-06, .270 Win, .280 Rem, .338-06 and .35 Whelen are among the most popular offspring but there are others. This throwback to a 111 year-old design remains among the most popular cartridges, particularly for hunting purposes.
The .30-06 fills a "niche" so large it is inappropriate to call it a "niche". I won't claim it is the most useful cartridge but I don't know of any cartridge that deserves the title more.
The.30-06 use for wildcats was more an issue of timing and lack of other available parent cases than anything. It doesn't reflect any efficiency on the part of the .30-06 - which makes sense, since the .30-06 is on the inefficient side for a bottleneck cartridge. As to case taper and shoulder angle, there is exactly zero advantage to a high taper and shallow shoulder at this point. It's just a waste of case capacity and needlessly decreasing the efficiency of the capacity you do have for no good reason.
