It seems like the developer key mode is not supported on the homekit version of the aqara hub (hopefully yet!)
One of the admins on the company’s forums mentioned a timeline of early 2019 back in September.
It’s a wait and watch scene right now!
Was literally about to buy the new gateway since the price difference b/w old one and this one was negligible.
However now trying to figure out if I should expect aqara to stick to their promise or just go in for the old for now and then upgrade later.