Does open source allow the community to advance webOS on old hardware and make custom updates? Or just will help future possible devices? I am confused how the app store etc will go on etc.
My guess is it would be mostly future as it will probably take awhile for the to convert webos over to open source and by then a lot of the current hardware will be on its last legs.
if this was the case though why wouldn't they just keep the OS for themselves then?
Money. HP didn't want to invest trillions of dollars in the platform. Open sourcing allows smaller developers and manufactures to put work into the platform and use it for whatever purpose you wish. This is not only the cheapest option, but the best. WebOS can grow so rapidly now. And HP seems committed this time, which is good.
WebOS needs work but not a "massive transformation". The card based UI is staying, you being that it's what most people are interested in. If you get rid of the card UI, you have Android.