Unicode in the equations: pros and cons

The pros and cons are pretty much the same as they ever were. Old timers like myself have a built in familiarity with ascii based markup, but I suspect that this will seem increasingly anachronistic as we move further in to the 21st century. Web based tools (and as Count Zero noted) Word processing systems and increasingly command line shells of common operating systems have a natural Unicode handling, and I suspect newer users will find it harder to accept restricting to an ascii character set.

There was a time that the general feeling was that people should use \"{o} or \'e markup "for portability and ease of editing tools" rather than use ö or é but now I suspect that more or less anyone writing non English documents uses [latin1] or [utf8] with inputenc or uses xelatex or luatex and native Unicode input.

Despite the above, there are some advantages to using markup over direct character input, other than just familiarity for people who grew up using punched cards. One example that it is much easier to check that various document norms and conventions are upheld. For example if you want a particular arrow style it's probably easier (by eye) to spot (say) \longrightarrow than to recognise the multitude of different Unicode arrows. Also it depends on your tools, but for most of the tools I have it is still quicker and easier to type \longrightarrow than ⟶. But note that editing tools can completely lose the distinction, allowing you to type \longrightarrow but entering ⟶which is one reason why I suspect, as noted above that Unicode in files will become the norm.