According to What do user trust levels do?, users who have been suspended within the set time period cannot be TL3 (and will lose TL3 if suspended). However, blocking is not mentioned in the #faq, nor in the code (see below). I would like to propose that blocks by staff should have the same effect. If a staff member needed to prevent public posting by a user, they are not TL3 material at that time.
AFAIK members are manually Blocked by Moderators at that members Admin-User page.
On the same page is an option to Lock the Trust Level.
The line immediately before the highlighted one is
return false if trust_level_locked
That is, if the Trust Level is Locked, that member does not meet Trust Level 3 requirements.
What are you proposing that is different?
Unless I am missing something, suspending a user (or blocking them) does not automatically block their trust level. Further, if a user was suspended (or blocked), within the last 100 days, they are/should be prevented from reaching TL3, without staff needing to manually lock their trust level.
Is this not what currently happens for suspensions?