While I enjoy the uniformity the recent changes have brought to the forums the inability to set font sizes has left us completely unable to format documents properly according to any type of standard. This is a pretty major issue in longer posts, it's not easy to pick out different sections of a document when we neither have the ability to create a linked Table of Contents or make section headers stand out more in comparison to section bodies.
My recommendation is allowing us to use the html header elements (h1 - h6) or a subset of them with associated styling that keeps in line with site's own standards. With a drop-down containing selections for different html header elements labeled for their purpose. On a private forum I assist in operating, our BBCode for heading elements looks like this:
[head]Text[/head]
[shead]Text[/shead]
And the output ends up being:
<h3>text</h3>
<h4>text</h4>
We also use:
[hint]text[/hint]
[disabled]text[/disabled]
Which just changes the text colour to a lighter shade of grey to de-emphasize various parts of the post. The output as you might have guessed looks like this:
<h5>text</h5>
<h6>text</h5>
Using these few basic elements for formatting purposes would give us the ability to do more when formatting longer posts or documents and still keeps everything uniform with the site's style.