I have been away from home recently, and so missed out on this discussion: Cardinal Sarah's challenge to traditionalists (and also here).
I do think Cardinal Sarah's language of "liturgical reconciliation" is a very useful one. After all, in the original context of Summorum Pontificum, the opening created for those with an attachment to the Extraordinary Form to have a more natural place in the life of the Church was a key strand in Pope Benedict XVI's intention, and I recall Pope Benedict at the time being spoken of as a "Pope of Christian unity". Indeed, it is a language used by Pope Benedict himself.
I also feel that, beginning very shortly after Summorum Pontificum, there has been an intransigence on the part of leadership among the organisations manifesting attachment to the Extraordinary Form towards another key strand in Pope Benedict's intention. Cardinal Sarah has addressed this in his recognition of the need for a genuinely mutual "mutual enrichment", rather than a one-sided movement towards a more traditional liturgy. This is something in which traditionalists have shown little or no interest.
And I think Cardinal Sarah has correctly identified the adoption of a common calendar as an essential step. One cannot speak of "two forms of the same rite" without a common calendar - and traditionalist resistance to this seems to me to represent an opposition to the principle of two forms but the same rite. The process can be genuinely mutual - adoption of the newly canonised saints and the simplification of the liturgical seasons might go alongside a restoration of the Octave of Pentecost and a permission for double collects so that the celebration of a Sunday does not abolish entirely the celebration of a coinciding saint for that year.
It says a lot that, even ten years after Summorum Pontificum, a suggestion by the Prefect of the Congregation for Divine Worship that progress should be made on mutual enrichment causes controversy. It shows just how far we still have to go for an authentic implementation of Summorum Pontificum, an implementation that is for the benefit of the many in the Church and not just for the benefit of a traditionalist few.