Being across the isle one can see each other. Talking is another matter. One may able to attract attention, but holding even a brief conversation would annoy nearby passengers to no end.
Holding hands across partitions is technically possible, but not comfortable at all. Wouldn't work for more than 1-2 minutes, which probably is all you need for providing takeoff/landing comfort.
Talking across partitions I don't think it would work too well. If I'm talking loud enough for 3K to hear me, why wouldn't 5K hear me too ?