I wouldn't. I would rip the formica off than replace / repair the
plywood and put a thin hardyback board on top before tiling.
While the formica is off I would check for alignment and secure
fastening to the wall and between cabinets.
But that's me :)
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Hi, I sort of figured that a HardiBack sheet would have to be used. I
would assume 1/4" thick would be adequate?

Naturally, I would have to take out both the Kitchen Sink Basin, and
Electric Countertop Range before proceeding, so adding Tile on top
shouldn't be a problem.

And I agree also about NOT using Stone Tile for a Countertop for the
reasons you state.
Also, Stone Tile would be very unforgiving should you tip over a glass,
or Coffee Cup on it.

I've tried talking her out of going with Stone Tile, and one would think
it would not be the best route to go. I honestly don't think I'm going
to take the job, as I might be getting myself into a real nightmare. If
it was me, I'd probably replace the entire Counter with Corian.
Thanks, Mark