Yes is time to consider a Vala 1.0 release. Vala 0.34 code generator and bindings support LTS versions of GTK+ 3.22 and GLib 2.50. Next stable version of GTK+ will be 4.0 and GLib 2.x, but they have to traverse through 3.9x versions and any GLib 2.x on the way. Reaching that point we can consider Vala 2.0 release.
Traditionally a new Vala version is released along with GLib and GTK+, with bindings updates, from them and other projects. Some times, is necessary to change some Vala syntax or implementations, like threats, in order to be in sync with current GLib/GObject/GIO features. Because this, may we can consider to increase Vala API each stable version of GTK+.
In order to reach Vala 1.0, may we should identify stoppers bugs before to go. Some of them can be related to GNOME Builder, but may is not a real problem is you don’t use it for Vala development. I really would like to file, find and send patches for some of them, producing warnings at C compilation, for a better experience.
A road map could be stated at Vala’s Wiki, in order to track that stopper bugs/features to fix/implement before 1.0 release. This will mark a good stand point for any developer using Vala.
Debian is around corner. It supply Vala 0.34, then it should be considered, and backport fixes, as a LTS version.