All of the College of Cardinal electors were appointed by either Pope Benedict XVI or Pope John Paul II. Both popes were committed to the holiness of the Tridentine Mass. I doubt that the next pope will retreat on their actions to promote regular parish celebration of the Tridentine Mass.
It is counter to the unity of the Roman Church to have two parallel Liturgies running side-by-side. It only makes those heretic schismatics continue their charades and pretend to be part of the Church when they think everyone else outside of their delusional group as "invalid" and "heretic".
I think I misunderstood this statement initially. It sounded to me like a criticism that would apply even to the existence of the Roman Rite, Mozarabic Rite, Ambrosian Rite, etc in the Latin Church.
But based on later statements, I guess your objection is just to multiple side-by-side rites in the same diocese?
(Perhaps you could also clarify what you mean by "the Roman Church".)
Roman Church means the Church of Rome, and those under her jurisdiction (Pastor Aeternus aside) and celebrates the Roman Rite.
Yes, people under the same bishop should celebrate the same Rite. I know there are issues with overlapping jurisdiction in many places, but that issue aside, if you are under the same bishop you should be able to go to any of his parishes and have the same Liturgy. At least on the same day. I even commented some time ago over at CAF that the OF can become some sort of "Low Mass" for "Ordinary Time" and the EF can be the "High Mass" for special Liturgical seasons like Advent, Lent, Easter, Solemnities, etc. But it should be uniform across all.