..is this restriction, which certainly was a good thing at the time, still relevant today?

Well, the only reason we are talking about the current /list implementation is because the OP reported an issue that turns out to be due to a server not sending the correct numeric reply.

Other than that, this feature has been working well with few, if any, reports of issues for a decade or more.

So I am not really inclined to make any changes to it at this point.