The only "DJ's" that will be negatively impacted by this are not real DJ's - in fact they themselves may actually use it.
If you are comfortable using a mic in front of a large group, actively engage with your audience, do some basic mixing of songs, bring some energy to the party - I don't think this will effect you at all.
I will say this, I've often considered putting my cell phone number out on the tables in the venue, with a note to text me requests, but I've never done it. I don't want to open Pandora's Box!
Real DJ's - are not all over the microphone or constantly engaging with the audience. That's called an entertainer, not a DJ. Big difference. DJs are all about the music.
I came from a night club background and in some venues we performed as entertainers, and others it was strictly the music and we were expected to avoid using the mic as much as possible to not intrude on the club's ambiance.
Real DJs are able to get the floor packed without saying a word and TrackTL
potentially takes the guesswork out of reading an audience. To that end a DJ could easily deploy it as prompter or request generator - not sourcing it, rather following it's lead.
I think TrackTL is yet another perfection of a trend well under way, though this is essentially crowd sourcing the music - something that can work well if popular impact is what you're after. Many events however are directed by the specific design of one subset of people and not left up to the crowd. This is especially true at theme events, or anything connected personally (birthday, anniversary, wedding) to one or more people.
The question remains for any event:
"what percentage of the audience actually cares to participate?" I regularly do events with hundreds of people in attendance. I don't get hundreds of requests - so, clearly people are not that interested in directing the music. Put a video screen with the current cue in place - and I think I'm going to get all the disgruntled or impatient complainers in my ear instead of the optimistic requester. Dealing all night with control freaks hoping to circumvent the cue would get old really fast.
Then comes the issue of what might really happen at gigs where it does garner large scale participation. Is it actually a dance floor killer? Will the high school dance become a high school stand-still where teen age zombies stand around texting on their smart phones and manipulating the video cue list all night instead actually dancing and socializing? TBD
People have always had the ability to hand the DJ a record, tape, CD, iPod, smart phone, etc with a given song they wanted to get played. Track TL simply removes the middle man and aligns you with the interests of the equally engaged people around you. Emphasis again - on that question of whether a crowd is ever equally engaged.