So with each TES game featuring each province of Tamriel,and with each game of the series coming out every 5 years,considering there are 4 more provinces of Tamriel we haven't visited yet,the exploration of Tamriel will be complete in 20 years by now,2032.

By then the series will be so old,that it would be reasonable to reboot and go for a 2nd pass through each province.

But that makes me wonder if we will ever get to play on Akavir.

If the current fashion keeps going,the closest we will get to play on Akavir will be in 2037,25 years by now.
That is assuming that they won't decide to do Atmora or other continents after Tamriel is covered.

What's your thoughts on the case,how do you think the series will handle the huge variety of places it have,with the time of every TES game taking 5 years to be completed ?

I really hope they don't do Akavir, as is I'm already disappointed in how their handling the Akaviri influences as is. Will they? I doubt it, since its completely unfamiliar, though its possible.

It's likely Akavir will be explored either as an addon to the MMO or as one of the last single-player games gamesas plans to make.

I doubt for the MMO. Your already not allowed to visit provinces not native to your race (or alliance), I can't imagine Akavir being on their slate, especially given the time period its set in.