Great. I always wanted this change. However, I'd prefer the singular Form over forms.

For field path and rule path, I'd suggest them to be inside this form folder like Form/Field and Form/Rule which IMO also agrees to the namespace pattern.

Eventually the PHP classes should move to a file path where they get autoloaded. But there is a fair bit of work needed with JForm to get there (including support for namespaced classes and deciding when we're going to do the B/C break of not having every core extension's form classes using the JForm class prefix).

Alright. I can't say I get that exactly. Since I've not yet stepped into 4.x dev I find myself ineligible to speak much. My joomla.todo is still filled with 3.x stuffs. All the best everyone here. I'll be catching up soon. ☺

An approach how to namespace JForm can be found in this pr #15893. I would not mix xml files and PHP classes in the same folder. Thats why the forms folder is lowercase and should only contain xml files. IMO the field classes should belong into the Field folder.

FWIW in the Framework repo we actually deprecated and removed in full support for looking up class objects using the file path lookups in favor of full autoloading support, so the only file path stuff left there is for the XML files (for obvious reasons). That should be our long term goal with the CMS, it's just going to be a painfully long transition.