Tcl Source Code

I researched and I found that PCRE is used in the PHP programming language, the Apache server and R. 
Source: https://en.wikipedia.org/wiki/Perl_Compatible_Regular_Expressions

I don't know whether it is a good idea to make a change . Anyway it's interesting to know what would be the increase in size, because I have understood that Tcl is normally used in embedded systems. For me the size is not so important but I imagine that for some users it is.

I suppose also that with this change then the Tcl developer's team can concentrate in other important parts of the language and be more focused.

What would be exact the impacts to this change?

I suppose that one of them is performance, for example in alternation expressions. Source:
http://lh3lh3.users.sourceforge.net/reb.shtml