bar end shifters on drop bars - why not run the cables all the way to the stem? The typical touring bike with drop bars and bar end shifters shoots the shift cable out the bar tape, right under the curve like so:


My bike is like this. It would be cleaner to run those cables all the way along the bars under the tape and have them come out alongside the brake cables. What's the problem with doing it like that? Too many curves in the cable makes too much cable drag?

At some point I'll re-cable everything - what would be the downside of running the shifter cables all the way to the middle of the bars under the tape to where STI shifter cables emerge?

(FWIW the way the cables come out as it is now, dealing with those cables when riding is a minor issue. But it's still an issue - there are times when you must open your hand to move it from here to there on the handlebars. Possibly the bigger issue to me is handling the bike when not riding, locking it up, etc.)
It will work, but you will add considerably more housing and 2-3 more bends in the housing.  The additional bends will introduce friction which will affect shifting performance, but it should be usable if the cable and housing are good quality and you avoid damaging the cable during installation.