Language mutates in several different ways. Sound mutation (e.g. the hardening or softening of consonants) takes place over a predictable generational period - accurate enough to be able to trace the historical beginnings of mutations. Words, as units of meaning, also reveal the precise time of two languages' earlier meeting, with meanings changed or differences adopted (loan words) or pidginized. Word elision also appears to increase with time.
Structural changes such as in sentence construction seem to be the slowest. A proto-IE speaker might possible recognize some branches of the modern IE family of languages.
What interests me is that the study of genomic mutation, language mutation, and archeology can now be cross-referenced to more accurately date migrations, however caused.
OTOH ATinNM will no doubt come swanning in and point out the inaccuracy of my insights ;-) He is, after all, Uncle Babel... You can't be me, I'm taken
And linguistic evolution in the future is not really predictable beyond a few already started sound changes. Un roi sans divertissement est un homme plein de misères
The feedback system for the exchange of meaning ensures constant pressure on language. In cultures where mass media saturation is high, these pressures are all powerful.
In cultures exposed for the first time, on a broad front, with another culture, these pressure are also powerful.
The only thing one can predict for the future is further elision of word and phrase length, because the process of mass acceptance of a shortened version of the meaning is now so rapid. You can't be me, I'm taken
Again, as long as the language can express advanced thoughts, how it expresses them is of no importance. All language, given enough vocabulary, can express those thoughts ; the "evolution" of language is never that a language dies because it can't express thoughts that another can, unlike biological evolution. There is no "fitness" of languages. Un roi sans divertissement est un homme plein de misères