A lot of this detail and worry is eliminated by simply asking BIP 102
maintainers to change to a different bit that works best for everyone.
Existing nVersion garbage will get buried in sufficient time window to
prevent anything from triggering.

Just settle on a specific standard, reserve bits for feature upgrade forks,
and move on.  There is already a rough standard proposed in sipa's gist.





On Wed, Aug 19, 2015 at 9:22 AM, Tier Nolan via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> On Wed, Aug 19, 2015 at 7:10 AM, Mark Friedenbach via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> We can use nVersion & 0x8 to signal support, while keeping the consensus
>> rule as nVersion >= 4, right? That way we don't waste a bit after this all
>> clears up.
>>
> What happens if XT gets 40% and this BIP gets 55%?  That gives 95% that
> accept the upgrade.  Version 3 and lower blocks need to be rejected after
> that.
>
> By advertising 0x7 for the last 3 bits, XT is effectively claiming to
> support the check locktime verify BIPs but they don't have the code.
>
> This sequence could be used, without a specific version-bits proposal.
>
> Until height = N + 5000, if 950 of the last 1000 blocks have the 0x8 bit
> set, then reject blocks with version numbers less than 8.
>
> At height N, if the above rule is active, then the BIP is permanent.
>
> It applies to any block with bit 0x8 set, once the 75% threshold is met.
>
> From height N + 5000 to N + 10000, reject blocks which have bit 0x8 set.
>
> N could be set 1 year from now, or so.
>
>
> This gives a period of time after lock that bit 8 is kept and then a
> period where is is guaranteed to be zero.
>
> This gives software that is only watching the bit time to be upgraded and
> similarly time where the bit is set to zero before it can be reused.
>
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