That milestone number has been a while in the making. There will be some growth for Summer 2026 but nothing major as Ryanair and Jet2 have fairly minimal growth. The latter will have some A321neo's based but my understanding is they essentially replace the Titan A321 leases. Turkish Airlines is the main new addition and various other airlines will have some new routes/added frequencies. There's not much more can be done until the Terminal extension is complete as there's no capacity for additional based aircraft until then, meaning any growth in the meantime has to come from either some upguaging or away-based traffic.
Enabling work on the extension, including the relocation of UK arrivals and reconfiguration of the orientation zone post the security extension is essentially completed. The Escape Lounge will be closed off from end of February as that work progresses. Work on the main extension is due to begin this year. Based on current timelines it'll probably be S28, possibly S29 before any meaningful new capacity can be fully unlocked.