"IMHO, no one insisted on VFD and GPIB only."
You could change the VFD to any other display technology you want, glyph for glyph. The display has its own controller so that would not require any software changes, but doing so would not sell a single extra meter.
Changing what is displayed would require a significant investment in software modifications, and would probably not sell more than ten or twenty extra meters for them.
Changing the external interfaces to the outboard processor, would require a major investment in software, it is not "just" in any sense of that word, and it would probably not seel more than an extra ten or twenty meters either.
If Keysight wanted to do any of those things, the only sensible way to go about it is to get the RoHS meter out there to keep the revenue stream going, and then introduce a B model later, which has the same in-guard boards, but a different out-guard controller, frontpanel and backpanel.
Depending on the production and long term experience with the RoHS in-guard boards, and in particular actual customer feedback, (as opposed to various volt-nuts without purchasing budgets in some quaint but not revenue generating forum), they might also update the specifications at that time.
I do not expect that to happen.
(But again: If Keysight needs somebody with the necessary code-archaeology skills, I'm available :-)