Matt Corallo brought up¹ the issue of OP_NOP scarcity on the mempool
only CLTV pull-req²:

    "I like merging this, but doing both CLTV things in one swoop would be
    really nice. Certainly if we're gonna use one of the precious few
    OP_NOPs we have we might as well make it more flexible."

That said, if people have strong feelings about this, I would be willing
to make OP_CLTV work as follows:

    <nLockTime> 1 OP_CLTV

Where the 1 selects absolute mode, and all others act as OP_NOP's. A
future relative CLTV could then be a future soft-fork implemented as
follows:

    <relative nLockTime> 2 OP_CLTV

On the bad side it'd be two or three days of work to rewrite all the
existing tests and example code and update the BIP, and (slightly) gets
us away from the well-tested existing implementation. It also may
complicate the codebase compared to sticking with just doing a Script
v2.0, with the additional execution environment data required for v2.0
scripts cleanly separated out. But all in all, the above isn't too big
of a deal.