Since they keep coming up, here's an overview of some bad theories which I very much doubt and the reasons why. Please correct me if I'm wrong about anything here.
Using a keyfob/bracelet infrared camera and marked deck (video)
Doubtful for many reasons. First of all, for this to work the deck must be carefully positioned in front of the camera for a second. This requires the camera to be on the felt (not the rail), and for all dealers to be accomplices (On Stones Live, dealers are rotated out just like at any other poker table.) It also requires getting a special deck into the game, which would also have to be a functional RFID deck. Also, his actions suggest he doesn't know upcoming community cards (eg. always folding flop/turn with low equity, never calling and binking, folding when he would have binked, pot controlling when opponent has a lot of equity and waiting for brick turns/rivers rather than getting it in on the flop)
Reading the RFID cards
Not possible. The cards are passive RFID. They do not actively emit a signal and must be activated by the reader on the table. It wouldn't be possible to read cards across the table.
Hacking the table/Going solo
Doubtful. Postle has ties to the company that set up Stones Live stream, so a theory that he installed some kind of backdoor into the table that would send him the RFID info seems to fit. However, we saw Postle play humanly at times, that coincide with when Justin was away. If he did not need an accomplice he would be able to play perfectly the entire time.
Accessing the raw stream through Twitch
Nonsense. The raw video feed would not be uploaded to Twitch. The production crew enter the betting action in real time, then the commentators are shown that feed with the graphics overlaid on a 30 minute delay, then the feed with the commentary is finally streamed as it happens. It is not delayed on Twitch's end. So you wouldn't be able to see anything with Twitch credentials.
Using some kind of code or signaling device
This would make sense, if Mike was trying harder not to get caught. However we can see on the video that when he is godmoding he is always either looking at his crotch phone or wearing his baggy hat. Also, he doesn't just know when he is ahead or behind, he knows exact hole cards even when the hand is multiway. That much data would be hard to transmit with a basic signaling code. It seems much more likely that he is just receiving hole cards in clear text.