After several months, a drum student of mine still seems naturally to lead with the left, despite practising on a right handed set up kit. It was at my suggestion. I'm at the point where I'm considering changing the kit round. Anyone had similar experiences and solutions? I just feel for his future, it's better to put more effort in now, given that he's going to have far more opportunities to play on r.h. kits. Or go with the flow?
Personally I consider myself a left handed drummer despite being right handed in everyday life. I write and play guitar right handed, but on drums it always felt natural to play with my left. Back when I learned in school I led with my left and when we had the opportunity to play on a real kit rather than our practice pads I played open handed. I also played timpani and preferred having the low drums on my left.
I think the bigger issue is footed-ness. It depends on the genres he intends to play, but a lot of genres have complex and heavy bass drum lines that require dexterity in that foot. Another issue is if he wants to play with double bass drum pedals; that is strictly speaking the only drum set equipment that is not reversible, and there are not quite as many choices for left hand DB pedals as right.
For switching sets around I've never had much of a problem. Cymbal stands, snare, and floor tom are easy to move around. The only tricky part is the rack toms since they will likely have to be readjusted height and angle wise to fit over the bass drum. This is more of a problem if the toms are mounted on the bass drum rather than on cymbal stands. Racks can also be really annoying, as would microphone set ups.
I'd say let him try it out and watch his bass drum foot to see if it can keep up. If he really feels comfortable playing that way it's going to be a lot easier for him to learn. Most gigs should give him enough time to switch a set around, unless there's not 5-10 minutes he could have. Bringing his own double bass drum pedal would be the only equipment he'd need to bring that's unique to a lefty setup.
Try switching the kit around for the guy, if you have not already - at least once to give him the chance of attempting to play the drums the way they were meant to be played when leading with the dominant hand... No harm ever came from trying.
Case in point, I played with a leftie on and off for a couple years (about 10 years ago.) He, however, played the drum-kit in a right-handed set-up. He did this because he "learned that way" and "always played drums that way" because of (according to him) the very reason you state: he had more opportunities to play on a right-handed kit over the years... After several instances of losing tempo (in either direction by speeding up or slowing down,) missing beats, and/or generally 'not playing well,' I insisted that he switch the kit around to accommodate his dominant hand... As a matter of fact, I did it for him (he was a stubborn artsy-type.) Saying that the difference was drastic is a complete understatement. In the couple minutes that it took to switch around the kit (including the rack toms and the double bass pedal,) this guy went from being 'just ok' to someone I might actually call a "drummer."
Now, this guy was not a drummer (at least in the same sense that I am not a drummer, hence the 'bassist' in my display name, even though I can play and write for drums fairly well.) We were doing another project at the time - he is a singer/guitarist. But, we liked to have fun while we worked and he could play drums. And after the switch, he could play them better than some others who I have heard call themselves "drummers." Seriously, it was like playing with 2 different people... I can't stress this enough. He went from 'bad' to 'good' almost instantaneously. It was embarrassing and we both laughed about it later.
Forgive me if I rant but, I am also getting tired of seeing some of these answers on this SE that one might pull out of motivational social media posts. "Do what works for you, man" or "as long as it feels good, it is good" and the like... I could start learning to play the clarinet by sticking it up my... nose. But, it does not matter how good I became at playing it that way. Someone that learned to play the instrument the traditional way would ALMOST ALWAYS have the creative advantage and higher level of skill - and, arguably, the more fulfilling musical experience. (Unless I am literally the one in a million through-the-nose-clarinet-player.) And, no music teacher would teach me to play that way or allow me to learn to play it that way no matter how much 'I like doing it like that.'
The instruments we use today are modern technology. They are manufactured and set-up the way that they are in order to be used as efficiently as possible. There may always be some novelty to seeing someone performing in some strange way; like playing piano while standing on your head. However, if anyone is playing an instrument in any way other than the way in which it was 'meant to be played,' then that person will LIKELY NEVER achieve the full potential of skill on said instrument (despite there always being exceptions to the rule.)