None of the good things you mention seem to require new investment in XML, I'm not sure what benefits you see in it.
Why not just maintain existing functionality in RSS, and at the same time design a new format than is modern, simple, and extensible? The modern format could be linked to or embedded within the legacy format as long as needed.
Newer clients could continue reading the legacy format while adding support for the modern format. Older clients would continue to work indefinitely.
This would allow a gentle transition and allow new investment in XML code to cease.
I'm not religiously against XML, but there are many practical benefits to not using it when possible.
It is an interesting thought. I think it's hard for me to imagine the benefits of moving on from XML overcoming the pain of supporting both formats for literally everyone involved (producers and apps), and RSS is, despite its shortcomings, quite mature. If you are proposing hanging additional data off of RSS with a link but continuing to fetch the RSS for basic episode data, I think it is self evident why that is fraught. And if you are suggesting having an alternative representation, I guess I worry about reliving the pain of the early days, with lots of format fighting and incomplete / incorrect implementations.
Chris, it's only intuition, i'd have to research RSS more to respond precisely.
However I'm impressed by the fact that you are thoughtfully considering the comments here and taking the time to reply to them. That's always a sign of a good architect, and I look forward to seeing the progress your team makes.
Why not just maintain existing functionality in RSS, and at the same time design a new format than is modern, simple, and extensible? The modern format could be linked to or embedded within the legacy format as long as needed.
Newer clients could continue reading the legacy format while adding support for the modern format. Older clients would continue to work indefinitely.
This would allow a gentle transition and allow new investment in XML code to cease.
I'm not religiously against XML, but there are many practical benefits to not using it when possible.