Windows 10 Mobile Build 14393.555 could be the next build if it passes the release criteria. Microsoft has compiled Mobile Build 14393.555 on 17th November and it could be the next cumulative update for Windows 10 Mobile.
It is worth mentioning that Windows 10 Mobile Build 14393.555 would be from Redstone 2 branch and it may or may not include any new features or major improvements. Seeing the slow development of Windows 10 Mobile, the next build won’t contain any major changes apart from bug fixes.
Are you still interested in Windows 10 Insider Builds? Even though it has no major changes.