I’ve heard of this working more as a retainer type situation. IE a bucket of hours that can be used in different ways. This type of thing can work well with a start up or company with a smaller product portfolio that doesn’t need 40 hrs per week of a designer. Usually this is a pretty limited arrangement. For example it runs for a year or two and either the company needs more design time or they don’t make it so they don’t need any design time.
Separately I had a similar arrangement with a small engineering firm that had a single designer and they hired me to mentor him. Basically spent time once a week together. I did it for a little over a year and then felt he didn’t need me anymore so I stopped it. Fast forward 3 years I ended up hiring him at Sound United, he applied, I didn’t solicit, and the entire situation ended up being amicable including me helping the firm backfill with some recommendations.