Add options to allow for higher viable title font size
Due to descenders (lowercase g j p q y, also to a lesser extent underscores and overshoot of other letters) font sizes have to be smaller to prevent letters from being cut off (as titles will not be rendered outside of the titlebar). Particularly an issue with shorter titlebars as the difference needed to fit descenders properly is 20% or more (when not changing fonts).
Additionally, fonts that have a low baseline (which seem to be most of them) don't allow for as large of font due to how text scaling works in titles (the bottom half of letters will be cut off while there is still space at the top being unused). A very easy way to see this is to compare Monospace Bold (low baseline) and Nimbus Mono PS Bold (high baseline, slightly higher than the rest of the font family). For instance using the 'Smallscreen' theme and for a size to only accommodate non-descenders, Nimbus Mono PS Bold can be set to 18, Monospace Bold can only be set to 12. I have my own window theme that's shorter, where the respective numbers are 15 and 9.
Option 1: Add a very granular baseline offset option(s) user-side. Note that there is a vertical offset option in thermerc files... but due to the circumstances it isn't very useful, and even if you expect users to know to manually select the right font choice+size it only accepts whole numbers and thus there might not be an acceptable setting (the value does not seem to be pixels, and thus a difference of 1 might be the difference between cut off at top and cut off at bottom).
Option 2 (and better fix): Add a themerc option to allow title text to render where no titlebar is present* and also over the window that it represents (assuming that is technically viable). Particularly nice with high-baseline fonts sized so their baseline is right at the bottom of the titlebar (or low-baseline fonts adjusted to be that way with option 1 which would be optimal).
An option to have some form of automatic baseline adjustment might also be useful, at least getting the general baseline of all fonts in a similar place so different fonts aren't wildly different. Although granular offset would still be useful here, particularly for window themes where the bottom of the titlebar isn't the intended (and aesthetically pleasing) baseline (such as Adept, R9X, Slimline). If themes provided a baseline offset that most fonts were automatically adjusted to properly meet, that'd be great.
*=present as in visibly. It'd be understandable if for technical reasons the title needed the titlebar (even if no pixels) or the window contents itself to render onto. As in the title text would still be constrained to the pixels already being used for the window/window decorations.
Title text either partially or fully outside of the titlebar is an interesting idea (like a vertical window handle+buttons on left/right but title is horizontal on top still w/no background) but that'd probably need a good outline to work well (not a simple shadow). And ideas using that likely bring up more issues (like for a fully floating title you'd need a maximized offset unless you also expect users to hide or simply not see the title when maximized)