Parallel sentence construction: "I have, and always will trust you"

First, you're right; this is a violation of the Conjunction Reduction rule.
Will and have take different verb forms: will trust (infinitive) but have trusted (participle).

Conjunction Reduction requires that they be identical.

• I can and will deliver it = I can deliver it and I will deliver it (identical infinitives)
  (can and will are both modal auxiliaries and therefore both take infinitives.)

So how come people say it, then? The answer is interesting. It seems to be a memory phenomenon. Consider the following set:

• I have and will do it. (terrible)
• I have and always will do it. (less so)
• I have, and, as far as I know, always will do it. (much less so)

.. and in speech, strong intonation and stress can render these still less ungrammatical,
to the point where one hears things like this fairly frequently.

There is an aphorism in syntax called "Zwicky's Law" that goes like this:

The more irrelevant garbage you put into an ungrammatical sentence, the better it sounds.

People have limited memory space for real-time parsing and analysis, and get distracted easily.
So when they're waiting for an infinitive and some parenthetical remark distracts them,
they may lose the pointer to the infinitive and accept a participle because it's correct with have.

But it's not appropriate in writing, because it's additional distraction for the attentive reader,
and reading what some people write is hard enough without having to load a debugger, too.