When the 805x was first introduced, it was touted as being source code compatible with the 8048. This instruction may simply have been included in order to support that claim. The 8048 series had considerably less in the way of on-chip and off-chip resources, hence, might have realized more benefit from the inclusion of that instruction than the 805x.

That would explain why XCHD was included. It does signify eXCHange Digits, right? That weakens the notion that it was a wasted opcode, right?

RE