This way:

1. system cannot be played
2. only in case of destructive halving: system waits for the recovery of network security

The immediate danger we have with halvings is that in a competitive market,
profit margins tend towards marginal costs - the cost to produce an additional
unit of production - rather than total costs - the cost necessary to recover
prior and future expenses. Since the halving is a sudden shock to the system,
under the right conditions we could have a significant amount of hashing power
just barely able to afford to hash prior to the halving, resulting in all that
hashing power immediately having to shut down and fees increasing dramatically,
and likely, chaotically.  Your proposal does not address that problem as it can
only measure difficulty prior to the halving point.

resulting in all that hashing power immediately having to shut down and fees increasing dramatically