before anyone answers, I'd like to give a right solution:
by starting infra you are occuping space in your planets, so if you're abusing the new 'impoorvement' by doing infra you are actually wasting buildable land in your empire: lets say you build 1000 RCs, you need around 4 empty planets for that purpose that will never be ezploited with infra, only for this abuse, you'd need to build much more than 1000 RCs to make it a profitable abuse, and that means a lot of buildable land wasted just to save cash & some endu, this is not a good deal, you can keep it at 25% penalty.
but by starting units you arent occuping any space of any class at all, because it's limitless, so you do the trick with 10k tranports and voila! in the nezt wave you do it wiht 100k transports, this is a great abuse!
a good deal.
So the penalty for cancelation of units should be really harsh, 40% or 50% like I mentioned.
And dont get me wrong, I'm not against this or other improvements, and I'm glad to see things moving so fast lately in the dev team, but the problem comes when 'our' devs start using their precious time to arrange our silly mistakes (yes building the wrong amount of units/infra is a silly mistake). In real life, if you are ordered to build a refinement station, and you deliver a museum, you wont get anything back ezcept a kick in your arse, same if you are ordered to train soldiers and you build tanks that nobody can drive 