There has been some research done on this but it has been found (so i've been told) to be a much more difficult mental task, and i've certainly not come accross an information in print.
This is why the KO is recommended if you don't want the extra mental strain that comes with the Hi/Lo. You're not really expected to move on to anything more advanced..
It wouldn't have any real effect on Ace Sequncing, but as a large part of AS is shuffle tracking, you'd be putting a lot of work in and missing a lot of the avalible advantage.
In honesty, all the advanced techniques are mentally taxing and difficult to learn. It's a big step between counting and them.
Additional side counts aren't really the answer. They will provide you with a few tenths of a % extra advantage (at least an A side count will), but nothing dramatic.
Aces have 2 different effects on how you play. For the purposes of betting they act like a high card (i.e. you bet more when there are more A's due to the higher blackjack probability) and like a small card for playing purposes (where you'll regularly consider them to have a value of 1). The premis behind keeping a side count of Aces is that you keep your count without Aces for playing purposes and adjust your count by your sidecount for betting purposes. I've not looked into this at all, but i don't see that working with an unbalanced count.
As i said before, unbalanced counts with designed with the idea in mind of keeping it simple. If you really want to gain a greater advantage, you pretty much need to move to a balanced count. I'd suggest the Hi/Lo. It's the standard if you want extra 'bolt on' packages.
I think switching to Hi-Lo is a fine idea. My point was that if you want to retain working knowledge of an unbalanced count to use in situations where you want to exert less brain power, then I think learning TKO is better option for someone who already knows KO.

Switching back and forth between KO and Hi-Lo is probably not a great idea, since you'll screw up counting/not counting the 7.
I agree that if all they were looking to do was use an improved counting system TKO is the better route - let's be honest, they've already done most of the work and it saves re-learning point values, but that's not what they are looking to do.
Now i understand that the current playing conditions don't allow for anything more than counting, but the improvement between the KO and TKO or even Hi/Lo is small. My view is that although i may not be able to use a specific technique today, who knows where i'll be tomorrow and what game conditions i'll face, so i learn what i feel will benifit me the most.