It looks like Ceropegia woodii, but if it is, I'm surprised the owner didn't recognize it.

I have a lot of Ferocactus (I'm not sure about the species) seeds. I got them fresh off a mature speciemen which is about 3 feet tall and a foot in diameter. Its a great looking specimen . If this interst you, please suggest a trade ratio.

Some Brachychiton (bottle trees) have similar leaves. There are hybrids offered, so I am not certain at this young age, and sans a flower photo, of a more specific id. Sometimes the leaves change form as the plant matures. I am more familiar with Brachychiton when they are mature. Or maybe someone has a completely different id idea.

you cant take a plant that has been indoors for 10 years and stick it out in full sun ... without properly hardening it off to such ... but if you were to cut it down to just above where the new shoot is.. then it wont have any leaves to sunburn.... so you might get away with it ... and since you will have a big piece ... see if you can propagate/root small pieces .. and start new .. and if you do that .. then i would just throw out the old plant ... since you cutting are the old plant .. you arent losing the plant ... if its not obvious.. it is severely pot bound ... and i wonder if there is actually any potting media in that pot ... which means you probably have watering issues [especially if you put it out in full sun] .. which is probably why the leaves are so off color.. if not for all the accumulated salts in the old media ... ken