If you want to keep transparency, then I find .png the most convenient now . You can also use .tif.
Without meaning to decry your suggestion, I would personally rather see effort first put into improving the main functions of the program (some of which don't work properly!) rather that provide features that can be handled far better by external programs, some of which (GIMP for example) are free. Windows is a multi-tasking environment so you can have both programs
open, and you can also drag and drop graphics from a windows explorer
window onto the timeline of Studio.
This is my personal opinion. Feature requests of this sort often draw
responses for both ends of the spectrum - some people want the moon on a
stick for $100, other shout "Fix the bugs first"
However, for marketing purposes, your suggestion fits in with the way computing is going. People expect "turnkey" programs or suites that do everything. I have two programs from Serif which I find are both excellent. Page Plus (for desktop publishing) is powerful, easy to learn and stable. It also includes a mode for Web publishing. However, the web publishing features aren't quite powerful enough for my aspirations, so I've ended up buying Web Plus as well. Both have simple image editing tools, but the programs integrate with all the others from Serif and both can link with Photo Plus for full blown image editing. The main advantage of this approach, (apart from more sales for Serif) is that the user doesn't have to get involved with the operating system. The way I've learnt to use computers (i.e. before Windows), the miracle of Multi-tasking is enough, and I'm not inclined to replace my ancient edition of Photoshop with Serif's offering.
The other advantage of this approach is that if I were a Serif customer coming to Video editing for the first time, I'd almost certainly buy Serif's offering.
I'm only the messenger about the plug-ins. The developer Harold Linke is still around on this forum 