In this current SSPX.org announcement, the SSPX refers to Maria Teresa Gonzalez Quevedo as "Venerable."

https://sspx.org/en/news-events/calendar/ven-teresita-quevedo-girls%E2%80%99-camp-45049

Problem: That title was given to her in 1983 by JPII.

Is the SSPX incrementally moving towards an acceptance of conciliar saints?

Of course they are: One cannot be accepted by the conciliar church while rejecting its "saints" (that would be resistance, you see, and as Fr. Cottier explained upon his conquest of Campos, "What is important is that there no longer be resistance in their hearts.").

But what does it mean to be considered venerable?

"In the Catholic Church, after a deceased Catholic has been declared a Servant of God by a bishop and proposed for beatification by the Pope, such a servant of God may next be declared venerable ("heroic in virtue") during the investigation and process leading to possible canonization as a saint."
https://en.wikipedia.org/wiki/The_Venerable

But has not the SSPX of old expressed serious reservations on this new conciliar concept of "heroic virtue?"

See this 2011 article from Fr. Gleize (SSPX) explaining new and redefined concept of "heroic virtue" (scroll down to "Third Difficulty: Heroic Virtue):

http://sspx.org/en/beatification-and-canonization-vatican-ii-3

Little by little, the SSPX is moving from integral Catholicism to integral conciliarism.

Canonisations are infallible. Still not sure how you can call someone a true Pope but reject their canonisations.

Holy Week was destroyed by Bugnini under Pius XII in 1955.
John XXIII inserted St. Joseph in to the Canon, removed the second Confiteor and some other changes I think. Someone else knows, I’m sure.

Tell that to all the Catholic saints and theologians who teach otherwise.

Evidently St. Thomas Aquinas himself teaches "nonsense".

Aquinas:
It's one thing if you respectfully disagree, but quite another in your hubris to denounce this common teaching as "nonsense".  You cross the line from theological opinion into grave irreverence.

Tell that to all the Catholic saints and theologians who teach otherwise.

Evidently St. Thomas Aquinas himself teaches "nonsense".

Aquinas:
It's one thing if you respectfully disagree, but quite another in your hubris to denounce this common teaching as "nonsense".  You cross the line from theological opinion into grave irreverence.

It's a classic tactic of his, and some users here who seem to be his disciples, to defend their beliefs by accusing others of believing the same. Here's a typical scenario you'll often see on Cathinfo: A sedevacantist says if you believe Paul VI was the true Pope then you cannot condemn the Mass he promulgated as impious and unholy, an R&R replies "then why don't you go to NO masses!", completely ignoring that the sedevacantist doesn't share his belief that Paul VI was Pope. I've seen that exact same scenario play out dozens of times. I'm not saying that there aren't valid counter-arguments about the claim the sedevacantist character made in that scenario, but instead of those actual points we usually just get fallacies, like the one I described above, and trying to point out the fallacy just leads to the entire topic getting derailed.

Almost makes me wonder if it's an intentional tactic to dodge the issue.

For some.  For others?  I believe intentional and of bad will.

I was the one who posted on SD about starting up Archbishop Lefebvre's canonization process. There was some opposition, hardly unexpected, but also some support, and there is a prayer thread dedicated almost exclusively for it. There's also an ongoing Rosary crusade where we've come to 2800+ Rosaries. Archbishop Lefebvre will be recognized as a Saint one day. I wish those who had that conviction would already begin asking his intercession. Recently, Archbishop Sheen's beatification process began with a reported miracle.

Why? Because many, many people were asking for his intercession. So in one case, God answered. I wish all would do the same for +ABL.

As for canonization, is it infallible? The question is nuanced. Does the Pope say the person canonized is in heaven? Yes, most definitely. Anything necessarily more than that? The Papal canonization decree only says that the person is in heaven and is to venerated by all.