I don't have a preference for creating this forum or not, but had some thoughts about trying to manifest/maintain one.
There is often confusion between Epiphyllum and epiphyte. Then there's confusion about the common name night-blooming Cereus, often attached to E. oxypetalum, and has a lengthy article on Wikipedia, detailing the cadre of diff plants that wear this moniker.
It might be difficult to name or briefly define the focus of such a forum in a way that everyone understands its' focus (who doesn't necessarily spend hours per week delving into taxonomy.) Even for those who do, the ID of even the genus of many of these plants remains a mystery for yrs sometimes unless/until they end up blooming. The common name orchid cactus is used to refer to other plants besides Epiphyllums, and there are many plants out there that are hybrids between an Epiphyllum & plants from other genera.
(Dragonfruit is a diff genus, and there's another Wiki article about the plants referred to by that name.
If created, I'd try to participate as much as possible, though these plants haven't generated much fodder for convo for me. After about 3 yrs, still waiting for E. oxypetalum to bloom, and may or may not have other Epiphyllums. Waiting for blooms to discover what some shared pieces might be. An Epiphyllum forum would be unique to ATP.