As many of the WS4 extensions are out of date with respect to their underlying JS libraries, in the first/current batch, we only released core bindings (covering charting, math, etc.) that have been updated to match their latest JS counterparts, giving a solid base to build applications with.

I suspect there will always be bindings that "are outdated but work", these can be retargeted to the latest WebSharper pretty easily, we just haven't done so yet. I guess it would be desirable to keep all extensions (~100 packages and growing) up to date, and this is where any community help is greatly appreciated. On that end, we moved the CI behind the WS5 packages to GitHub Actions, so it's more transparent and outside help is easier to give.

As for SlickGrid, the public repo is here. You can try to update the dependencies and the bindings and compile for WebSharper 5, or simply just use the WIG definition in your project directly for the time being.

You can, as you say, also use WebSharper UI's reactive capabilities to render tables (I'd suggest using templating through external HTML files for the most flexibility) for sequences of composite data (ListModels, etc.). It's not only viable, it's your best bet besides grid libraries, really.