- The BIP91 portion of the fork seems OK to me.  There are some issues with
timing, but since this is for miner coordination of segwit activation, and
has little to do with other network users, it could be included as an
option.   (I'm a fan of adding options;plugins, etc. to Bitcoin... some
others aren't.)

- This hard fork portion of the proposal is being deployed with "emergency"
speed... even though there is not an emergency on the network today that I
am aware of.   If enacted, it will certainly result in two chains - and
with no replay protection..  The results of this will be confusing - two
ledgers with many transactions appearing on both and others appearing only
on one.

- The BIP should be modified to provide evidence and justification for the
timeline that is consistent with the level of risk the network would bear
if it were enacted.

- The coercion used to drive production of this BIP is mired in a
misinterpretation of BIP9 and sets a precedent for Bitcoin that may
undermine the value prospect of all cryptocurrency in general.   For this
reason alone - even if all of the engineering concerns and timelines are
improved - even assigning this BIP a number could be considered
irresponsible.

- If you still want to code up a fork for the Bitcoin network, consider
starting with Luke's hard fork code and changing the rates of growth as
needed for your desired effect.   Also you might want to read this first
(code references are in there):
https://petertodd.org/2016/hardforks-after-the-segwit-blocksize-increase .
Plans are already underway for a hard fork, for reasons that have nothing
to do with block size, but could include a timeline for a block size growth
consistent with global average residential bandwidth growth.