With so many options available I do not think Speed Tree is a fundamental Middleware solution nowadays.
They will never provide the tool for free, everything they do is promotional.
You will never have a free Speed Tree for ever. This will always be for a limited time ever.
But with so many wonderful procedural vegetation assets in the marketplace using only blueprint.
I think speed tree is becoming increasingly worthy of better promotions to attract buyers’ attention.
And there are many other options without subscription like the plantfactorie.
Anyway, the only interesting thing in speed tree is its integration with the Unreal Engine LOD system using billboards sprite sheets.
But nothing impossible for a probable procedural tree plugin that can be fully integrated within Unreal Editor.