On September 30, 2015 5:26:51 PM PDT, Rusty Russell <rusty@rustcorp.com.au> wrote:

Gregory Maxwell <gmaxwell@gmail.com> writes:
 I can, however, argue it the other way (and probably have in the
 past):  The bit is easily checked by thin clients, so thin clients
 could use it to reject potentially ill-fated blocks from non-upgraded
 miners post switch (which otherwise they couldn't reject without
 inspecting the whole thing). This is an improvement over not forcing
 the bit, and it's why I was previously in favor of the way the
 versions were enforced.  But, experience has played out other ways,
 and thin clients have not done anything useful with the version
 numbers.

 A middle ground might be to require setting the bit for a period of
 time after rule enforcing begins, but don't enforce the bit, just
 enforce validity of the block under new rules.  T
 hus a
thin client
 could treat these blocks with increased skepticism.

Introducing this later would trigger warnings on older clients, who
would consider the bit to represent a new soft fork :(

So if we want this middle ground, we should sew it in now, though it
adds a other state.  Simplest is to have miners keep setting the bit for
another 2016 blocks.  If we want to later, we can make this a consensus
rule.

"Bitcoin is hard, let's go shopping!"  "With Bitcoin!"  "..."
Rusty.