Not everyone does it, and it’s ahistorical, but I think it’d a cool way to distinguish between voiced (ð) and unvoiced (þ) dental fricatives. Why not have two different symbols for these? Eg: ðe þin faðer þinks about ðis (the thin father thinks about this).

It’s not necessarily hard to type, on my computer it just happens to be AltGr+d (ð) and AltGr+t (þ).