The iPad is already one of the best creation tools out there for artists, musicians, photographers etc.
I’d suggest the iPad is hampered more by the limits of iPadOS’ multitasking UI and it’s roots as a scaled-up phone OS - and the scarcity of truly pro-level software - rather than the App Store and not being able to sideload.
In fact the only real reasons to sideload or jailbreak at the moment are to get around the limitations on running dynamic code - or to use cracked/dodgy versions of paid apps.
Wouldn’t be surprised if we see some big improvements in the dev experience over the next few system releases, but to say this will enable a burst of creativity is ignoring all the highly creative ways it’s already being used.