*cough*Cough* remember "Cyborg Monday".. I would NOT get your hopes up too much.
My guess would be "Soul trade" has NOTHING to do with trading souls i.e. swap, convert, exchange. But perhaps rather "Trade" as in profession, craft, etc. Possibly a character name...
I highly doubt NF would EVER implement ANYTHING to allow users to actually exchange souls. At most they might, on a slim chance, allow something like 1000 regular souls for 1 rare soul or 10000 regular souls for 15 fragments of some character. But even that is reeeeeealllllly going beyond what I've seen this company supply players with.
NF seems to have the mistaken mindset of "make it rare and they'll spend." rather than the more favorable "make it fun and they'll spend." I've posted a couple times that they should make characters much easier to acquire, then make the power ups more difficult to get and offer THoSE for $$$ (like talismans, skill shards, etc). If players actually GOT characters.. they'd be more likely to spend to power them up as opposed to spending for some random 0.1% chance at a character.