Well let's get this straight, right now every Type is going to get new Pokemon for it, the problem is with the balance, let's take a look at ALL the types and then how many of those types were in that Generation:
Types - Gen I - Gen II - Gen III - Gen IV - Total
Normal - 24 - 20 - 18 - 18 - 80
Fighting - 8 - 3 - 7 - 7 - 25
Flying - 19 - 19 - 12 - 15 - 65
Poison - 33 - 4 - 5 - 8 - 50
Ground - 14 - 10 - 13 - 11 - 48
Rock - 11 - 7 - 12 - 7 - 37
Bug - 12 - 10 - 14 - 11 - 47
Ghost - 3 - 1 - 6 - 9 - 19
Steel - 2 - 4 - 9 - 11 - 26
Fire - 12 - 10 - 6 - 5 - 33
Water - 32 - 18 - 28 - 16 - 94
Grass - 14 - 10 - 17 - 15 - 56
Electric - 9 - 8 - 4 - 7 - 28
Psychic - 14 - 10 - 20 - 9 - 53
Ice - 5 - 5 - 6 - 6 - 22
Dragon - 3 - 1 - 9 - 7 - 20
Dark - 0 - 6 - 10 - 7 - 23
Now by total, the type that needs a few more Pokemon would be Ghost-, Dragon-, Ice-, Dark-, Fighting-, and Steel-types. However, instead of going by total, let's follow recent patterns and you'll get a different story. As it turns out, Poison- and Fire-types have been decreasing each generation. Normal- and Water-types have been decreasing in number as well but they still have a healthy amount in each generation to not have this be a crisis to them. Ghost-, Steel-, and Dragon-types, who by total have a low amount, in actuallity are increasing each new generation. As for the other types, they have either been balanced or the last two generations they have balanced out. In my opinion though, types like Dragon-, Psychic-, & Steel-types shouldn't really be growing as these are powerful types and I think keeping them within a small number helps give this message off as well as give others struggling types more Pokemon to be their type. And while it is easy to make Water-, Grass-, Ground-, and Normal-types, they have a healthy number in the recent Generations so I think they should stabalize those so about the same number that was released in Generation IV should be around the same number as in Generation V. Finally I think we should have more Ice-, Fire-, Poison-, Bug-, Dark-, and Fighting-type Pokemon.
Oh, you think this post looks complicated? You haven't seen anything yet, wait till Friday, I'll have something that'll be quite a read.