For stain treating that would be great.
While reversing isn't really necessary (I mean, think about it, what would reversing spin direction change about laundry position?) the system could be manually added quite easily.
You'd have to make sure the pump wouldn't drain away the suds.
Using a valve to block flow to the pump and then adding a second electrical pump wired in the spin circuit of the motor would be an option, but I think the SQ drain pumps don't like running dry.
But I might be wrong.
Other option would be to use a diverting switch over valve after the pump.
Then use a switch and wire the valve in with the slow spin setting.
With the switch activated, during a low spin cycle, the valve would divert the drain flow back into the tub.
You'd fill the machine with a gallon or 2 of warm water, add your detergent, flip the switch and run a slow spin cycle.
Afterwards, just set it to the desired cycle.
However, using to much water might cause premature belt wear as it would keep slipping during treatment like during spin drain.
On the electronic machines of the current generation, I don't think that would work.
Me thinks that on these the drain isn't times but controlled via pressure switch and that probably would keep tripping with any water left in the tub.
And wiring the recirculation pump in would be tricky as the drain pump cycles on and off AFAIK.
This action could not be used entirely instead of an agitation wash method though or at least not effectively.
In theory, yes, it could result in equivalent results, but time would be more in the hour range for the wash alone.
Problem is that laundry would stay static during this action. No flexing of the fibres would happen.
Thus any soil that is present as one bigger mass sticking together (like a stain) would probably be hard to remove.
That pre-treatment method wonderfully loosens smaller stains up and certainly attacks bigger clusters of dirt.
That is why the Catalyst and for that matter many WP HE TLs with recirculation do that treatment before the agitation wash.
It's like using a stain pretreatment spray on the entirety of the load but without any waste.
But agitation would still be needed.
