With the default implementation of the enhanced toolbar as the default it is causing some issues at English Wikisource, and presumably other Wikisource languages.
In the Page: namespace at Wikisource, we implement part of the ProofreadPage extension. Part of the implementation is an addition of five buttons to the toolbar. Functions are
- toogle header/footer
- zoom in
- reset zoom
- zoom out
- toggle vertical/horizontal layout
these do not appear with the enhanced toolbar and I cannot fathom how <s>either, where they are added and</s> how to implement them into enhanced toolbar.
Reedy has shown to me that they are called in proofread.js  and I either need to know whether the modifications should be made to that script so that the buttons show up in enhanced and standard toolbar. Alternatively whether there is the means to add them to the enhanced toolbar outside of the extension. The former would be preferred as that would then apply across all the WS wikis, the latter will suffice and each wiki would need to undertake
On similar note, there is an OCR tool button that can also be added to the standard toolbar  that has similar issues.
If this is about guidance about how we fix locally, then we give it a go, just not either my comfort zone or knowledge base.