There is absolutely no drawback in using lexical binding. Since Org
9.0, it _is_ the default for Org core: almost every Org library
activates it nowadays.

Again, lexical binding has _no_ drawback and makes life of developers
easier (e.g., code is more readable, compiler reports more errors).
I moved almost every library in Org to lexical binding, some changes
being trivial, some painful, for a reason. I don't want to do a step
backward in that area without a very strong reason–to tell the truth,
even a strong reason wouldn't convince me.

Here are some of my observations on the topic of lexical-binding by following emacs-devel closely for the past few years.

I have seen this movement started on emacs master for a long time now (since 2011), and still there is a continuous effort to enable lexical-binding on more and more emacs core files: http://git.savannah.gnu.org/cgit/emacs.git/log/?qt=grep&q=lexical-binding

The same applies to Magit and many other external emacs packages ( https://github.com/search?q=lexical-binding+language%3A"Emacs+Lisp"&type=commits ).

The idea is that once almost all the elisp code out there is lexical-binding compatible, the default of emacs can be changed to that and dynamic binding can be obsoleted.

I have also seen how a lexically bound package is more portable as there is no implicit reliance on global variables from multiple other packages.