I have the free upgrade but only downloaded it for Layout 2019 since zooming in/out is less painful in 2019. Sketchup 2019 barely changed anything. IIRC their huge reveal was dashed lines. Wow. Amazing. Does this mean most or all of the plugins should still work in 2019? Plug-in compatibility is the reason I didn’t upgrade right away.
If the extensions needed updating for SketchUp 2019, most have been already so when you install them from the Extension Warehouse , Sketchucation, or other sources, you should be getting the most current versions of them.
If you were thinking of copying them from your SU2018 installation, don’t. Well, unless you enjoy chasing load errors. Some extensions did need updating for SU2019 and some just don’t install correctly if you only copy and paste.
BTW, there are other improvements and additions in SU2019 besides just dashes. It’s funny to me that people complain about the addition of Dashes to SU2019, though. This is a feature that has been requested since at least SketchUp 4 (pre-Google days).
Generally all small and simple extensions should work in all newer versions, given they are of good quality. More advanced extensions that use complied code for heavy calculations or to protect intellectual property, e.g. renderers, need to be updated.
And one other, more subtle, change caught me and Steve Baumgartner out in Angular Dimension 2.
SU used to show metric dimensions with no space before the unit - thus:
10mm, 5cm, 3m etc.
Now in v2019 it puts a space before the unit:
10 mm, 5 cm, 3 m etc.
So if you are putting back into a dialogue the user’s last input for re-use, unless you are careful, it won’t work in older versions of SU when input is expecting a length, and you have Model Info/Units/Display Units format checked. Versions before 2019 don’t expect the space, and complain that it isn’t a valid length.
SU 2019 code internally ‘knows’ this so the problem doesn’t arise there.