I vote no. Peacock eels reach a decent size, and one of more commonly available peacock eels is Macrognathus siamensis which can reach anywhere from 10 inches to 14 inches. They do spend most of their time in one place since they are ambush predators, but I am not really a fan of a 14 inch fish in a 30 inch tank. Macrognathus aculeatus is a bit smaller, but still it it kind of a stretch for the term in my opinion.
As for the potential bigger tank, in my experience and opinion, it is a lot better to not buy species for a tank you don't have yet. A lot of life can happen in get in the way between now and "probably in the future."
They are not especially fast growers though generally. Generally, they are around 4-6 inches at the time of purchase. If you are certain you will upgrade, you could try it out as long as you are ready for care if you want to. Honestly, they are a bit fragile and difficult to keep alive long term. It is quite common for people to really only keep them alive in a community for like a year. I would vote on waiting for your tank upgrade. Up to you though.