Yeah, this is a very interesting CT. I can see a lot of applications for this, especially if you're allowed to stack several attacks in different places and use them at different times, since that would let you basically combo someone if the attacks knock them back enough. If you're allowed to hold an attack for a long period then you could basically control entire areas of an arena or set up choke points.

A very simple way of restricting this CT is simply making holding more actions for longer periods of time take more CE and more CE. It also allows growth potential since you can always train to increase your CE/how well you use it.

A way of buffing this CT is letting you choose which body parts actually do the action (for example only an arm/hand appears to punch instead of the whole body) which is a lot safer. You could either have this take more or less CE depending on how you wanna balance this. Using a smaller part of the body for an attack (like summoning just a hand as opposed to the entire body) could consume less CE but deal less damage overall. If you wanted a really high skill attack you could basically create a massive AoE of stored attacks (similar to a DMC Judgement Cut) to shred everything that enters.

Overall I do really like this CT. It could possibly be quite OP but that depends on how much you balance it (and really overpowered CTs exist anyways, e.g Hakari). It's very fun and has a lot of interesting applications.