There is one problem with this idea, that being the case of an undesired (i.e. accidental) thrust reverser deployment during takeoff after the go/no go decision speed (V1) has been reached. In this case, the crew would be required to continue the takeoff, because there may not be enough runway left to stop the aircraft, particularly in a "performance limited" case.
As I wrote in my original post, the interlock could work one way or another (lock out a reverser while at least one lever in forward thrust OR lock out forward thrust while one engine in reverse), based on which "decision" is considered to be safer.
Based on your comment it appears that locking out reverse while forward thrust is present is safer - even with limited runway of Congonhas, if the reverser hadn't deployed and PNF had called out "no reverse, no spoilers, no decel", the crew would have all the time in the world to initiate a go-around. Partly because they would have lost noticeably less speed by that time, partly because they wouldn't have had committed to landing because of reverse thrust - they would have had an "out".
It would have taken a while to figure out the reason for what happened, but they wouldn't have crashed. Ditto in the case of uncommanded reverser on takeoff after V1.
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Actually, I was originally tempted to argue a case with statistics that even if the computer would make a bad call and decide to lock out thrust on TO after V1, then it would still be better than the current situation - because statistics apparently shows that uncommanded reverse on takeoff after V1 appears to be much rarer event on A320 series than mishandling of "the other" thrust lever on landing with one reverser inop.
But all this is irrelevant of course because the other decision (no reverse until both thrust levers retarded) (while shouting "retard, retard" at the same time) would probably indeed be safer overall. It would lean towards trying to bring pilots back into the loop instead of deciding for them. But I still think that no decision is worst choice of all.