I know mid last years if you had a 4 Port ONT and there were still ports available on the DP then you could order it.
When I was enquiring about faster upload speeds with BT's FTTP team, they told me I could order up to another 1 to 3 FTTP installs.
And when I asked if I would require additional ONT's and they did a check and said that no extra hardware was needed due to already having a 4 port ONT installed and the only hardware needed would be additional routers.
They went on to say that they just send the additional connections down that same fibre and that the ONT would send each of the additional connections to data port 2, 3 and 4, depending on how many I ordered.
But looking at the extra price required just to get the faster upstream bandwidth it wasn't worth it.
But like I said this was about mid last year, so stuff might of changed since then.
Paul