Thanks Johnson and Hampus for the clarifications.

However, I would rather do the opposite: soft-fork to 50% now, and soft-fork again to 75% discount later if needed, because it doesn't affect the max transactions/second.

Segwit as it is today should be activated. However if it is not before November, then for the next Segwit attempt I would choose a more conservative 50% discount.

On Tue, May 9, 2017 at 12:45 PM, Johnson Lau <jl2012@xbt.hk> wrote:

> On 9 May 2017, at 21:49, Sergio Demian Lerner via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>
> So it seems the 75% discount has been chosen with the idea that in the future the current transaction pattern will shift towards multisigs. This is not a bad idea, as it's the only direction Bitcoin can scale without a HF.
> But it's a bad idea if we end up doing, for example, a 2X blocksize increase HF in the future. In that case it's much better to use a 50% witness discount, and do not make scaling risky by making the worse case block size 8 Mbytes, when it could have been 2*2.7=5.4 Mbytes.
>

As we could change any parameter in a hardfork, I don’t think this has any relation with the current BIP141 proposal. We could just use 75% in a softfork, and change that to a different value (or completely redefine the definition of weight) with a hardfork later.