Could a Techdegree also be useful towards expanding a college CV?

It might be worth asking the college. However, I would expect that taking steps to learn and being proactive at expanding your skills and making achievements would all look good and of course, you build a portfolio in the mean time. And if anything, be beneficial in your own understanding.

But I think it depends on the college and what their expectations are. Unfortunately, some are more bureaucratic than others, in that they'll look to tick boxes on a piece of paper and they might be specific boxes. Or as I found when applying for Universities I had to have a certain number of UCAS points, which I got from my FE studies. So something like this wouldn't have helped me in that respect, but if in the hands of somebody who's using a little discretion and not just ticking boxes, it might help swing things more to my favour. I also know one of my projects at University, whilst fantastic and I had put a lot of effort into it, was marked down because I did not focus on the right criteria.

However, you might find that they favour extra curricular activities and to my mind it should make sense to. But I find no harm in asking and finding out what sort of things they are looking for.