1. Pattern doesn't change, and true enough, sinnoh had the same type of starters.
2. What do you think will happen when the elements or types changed? Obviously, many will hate it and some will not even buy the games, resulting in profit loss on the company.
3. Is it logical to destory the numbering pattern of the pokedex, like you would destroy the numbering pattern on the periodic table? Conclusion, the pokedex's pattern holds a nature behind it, just like the periodic table, with group 1 elements having the same nature and blah blah blah.
IT WON'T CHANGE... THOSE WHO TRY TO SPOIL POKEMON'S REPUTATION WILL MAKE FAKE CLAIMS OUT OF IT.