Progress bar in updatedb

No, there's no such option, as well it shouldn't have any.

If you need to measure that, you must first know how many files are present on your system, that means loop through everything twice, it can be slow

One evicent example is that if you extract kernel source code with file-roller, it's slower than doing the same thing with tar directly, because file-roller need to file out all files first(otherwise the progress bar might be incorrectly displayed), and you wait for a while before extraction process actually began.