If someone wants to put in the effort, by all means go ahead.
And I disagree with Hakumen's combos having changed a lot. While not as simple as "add jC", it shouldn't take more than 1-2 days to pick up the combos, and another few days to get use to the additional frames on j2C start-up.
Also, jC>gurren relaunch is not worth it outside of going for the kill. It's basically the same situation as blowing more meter after j2A (j2C) in CT, and similarly in CS. Either jC, land and get position below your opponent, or go a different combo for 5C knockdown. There are only a few situations where jC>gurren is required for knockdown, and those are usually due to uncommon launch starters.