What's the rush? Anxious to spend taxpayer money? Afraid the galaxy will go away or change rapidly?
Let's analyze what Hubble has collected (my understanding is that 80%+ of the pictures taken have not even been looked at) before we build the next generation.
You never know, perhaps we will find something in those pictures that would point the direction for the next space telescope.
As a matter of fact, yes.
For example, if the tools had not been in place for SN1987A, we would have lost a possibly unique view into distance calculations of the universe itself. There are once in a lifetime (sometimes once ever) events that would be missed.
And no I am not trying to "spend" money. Keeping Hubble alive will save money. Think of how much it will cost to replace it.