Does 10GBASE-R fully replace 10GBASE-X?
10GBASE-X is essentially obsolete. Four times the pins, four times the fibers or wavelengths, four times the traces, larger transceivers, etc. vs. 10GBASE-R. And no advantage besides lower per-lane bandwidth.

Now, there will be legacy hardware running this protocol, but only because nobody has bothered to replace it with something more modern.