My understanding around what you say, and what Karla has mentioned, around the hip angle and saddle positioning is more around fit. I assume that it is still working around a similar starting point of a fairly steep seat tube angle. Or is there a move to slackening seat tube angle as well?
DuncanM is basically right that a lot of modern TT positions are basically working with old road geometry, though saddles may be lowered - you might kill top end power but this is a TT not a road race, so you don't care about top end! A lot of the riders who use this sort of position have started off with a slightly more forward TT position before training themselves into it, so you want some flexibility either way - because a crunched hip angle can be fine once you've trained into it, but it does need a bit of training to be maximally effective. The training yourself into position is all part of training for the event though.
FYI My saddle positions are as follows. I've adapted my road bike fit to be more like my TT bike fit, i.e. slightly sub optimal when I'm using the road bike, but I'm doing it to train for TTs.
Road bike: 735 mm BB - saddle, 80 mm behind BB (actually currently 75 but only because I can't get it further back with the current seatpost). I might drop it a tad.
TT bike: 725 mm BB - saddle, 95 mm behind BB. It's an Adamo (i.e. noseless) saddle, but I do sit back on it rather than on the nose.
As above, it's probably best to experiment with fit on your road bike before investing in a TT machine. If and when you do go for a TT bike, basing the fit of your road bike and going for the smaller of two sizes if you're torn between them is sound. It's not the end of the world if you end up with a short stem, as frames are sized bigger than they used to be, because a modern TT frame can have a positive drag effect, so the bigger it is the better. If you have to fit a silly short stem, you'll probably look like a lot of the pros - except that if it gets too short, your front end can get twitchy. So yeah, get some clip-ons (though probably not a flip-forward seatpost, you shouldn't need more than a straight-up one) and see how you go. When you do buy a TT bike, get a cheaper one than you would and go for some aero testing if they're running again: I think a paired Aerocoach session (other providers are available) at an outdoor velodrome was £250 last time I looked, so it's the cost difference between spangly and not-so-spangly equipment on your bike, and should hopefully be much more effective.
