Please add an analogues of TeX ! to Math.
It will help to visually improve formulas.
Also it might allow creating longer arrows.
Feature requests are filed as ENHANCEMENT bugs to https://bugs.documentfoundation.org/. May seem strange. Is a fact.
This is the wrong place for enhancement requests. Write it into our bug tracking system: How to Report Bugs in LibreOffice - The Document Foundation Wiki. The field “Severity” has an item “enhancement” in its drop-down list. The “Component” is “Formula Editor”.
Only features that belong to MathML 2.0, Type Presentation Markup, can be included. Mathematical Markup Language (MathML) Version 2.0 (Second Edition) That is defined in the ODF 1.2 file format. There are lot of features of MathML 2.0 still missing in LibreOffice, which could -theoretically- be implemented.
Negative horizontal adjustment is possible in MathML, more information can be found e.g. in Presentation Markup
Stretchy arrows are possible in MathML. But the rendering engine of LibreOffice would need a lot of improvement, because it is ugly, if a normal character arrow is simply stretched. You see such ugly stretching in the brackets of a matrix currently.
Please make a separate bug report for each wished feature, otherwise it cannot be handled properly.
Thank you. The issue is closed.