I've been checking out the Android Scripting Environment, it looks rather promising. But is it a viable option to make a marketable app in? It seems like the customer would have to download ASE and then run the script from the environment itself.
Given the lack of responses, I'm posting this more as a bump and discussion opener than a complete answer. My take is that SL4A might be good enough for small scripts, but not yet for full blown apps to update to the market. Just browsing the last couple of months of the discussion group page (link here), it seems that the API is still changing quite actively. I'm posting some examples below:
If you have a great script that you want to quickly port to SL4A, give it a shot. But I would not replace java with SL4A at least until it gets an official release.