2 topics about the size of Scheme were posted on c.l.s. One was rather branch of other topic:How many R6RS users and how much code out there?. And the other is indirectly suggesting it: Question about vote of RnRS (the poster mentioned about the change between R5RS and R6RS as drastic change so seems it's about the size.) Even though all what I wanted to say is already said by Taylan on the first topic I've mentioned, I want to write something about the size so bare with me :)
The point of this topic for me is the definition of small or large. The poster said it is useful enough for educational purpose. I agree with it. If I need to add a bit of my opinion about this, I would say the languages which has proper design for the topic of the class are useful enough for educational purpose as long as students don't use convenient libraries. Java is fine for OOP, C++ is fine for OOP and meta programming, Mathematica is excellent for math, etc. So they can also be programming languages for educational purpose, right? Now are they small?
The answer for me is no. Especially if you see C++'s specification, it's more than gigantic even human beings couldn't understand, IMHO (are there people who understand all the spec?). I wouldn't say it's one of beautifully designed language, but it's powerful enough to cover other purposes including professional use . Then, should Scheme be this much huge to make all programmer happy?
My answer is again no. It's too complicated, it's piling up features on top of other features on top of other, lemme quit. One of the reason why C++ is piling up those features, I believe, is that it doesn't have enough abstraction to make language self growing. Most of programming language don't have this type of feature such as defining new syntax. Or if they have it, it'd be rather complicated to use, either deliberately or accidentally. If it's deliberately, then the designer of the language doesn't want users to use it casually. If it's accidentally, then it's not considered well but made rather adhoc. The first decision is understandable, sometimes those things are not really needed and don't want users to summon daemons from their nose.
Now what's the definition of small in Scheme specification? In my opinion, there is no need to pile up features but it can grow by itself. Let me elaborate what it means. Currently there're on going discussion about hashtable on SRFI. This might be a good example to do it. Is hashtable required by small language as Scheme? Well, my answer from bottom of my heart is yes but rational answer is no. Why no? It can be implemented by vector and record. Now one of the SRFIs also mentioning weak hashtable. This is rather interesting. Implementing this data structure can not be done neither in range of R6RS nor R7RS. So this seems required, right? Wait a sec, there's a draft SRFI about ephemeron. If you use this, then you can implement weak hashtable using vector, record and ephemeron. So the absolute requirement to have is this one. Hurrah, the language spec is kept small enough!
IMO, this is a bit too extreme. Each time users need to make own utility libraries for those common data structure is ridiculous. Then here comes R7RS-large process. The purpose, in my understanding, of this process is that keeping core language absolutely minimum and put a collection of those commonly used things in its specification. So implementations may or may not support all of them. Oops, again, what's absolutely minimum?
Unfortunately, I don't have generic answer for this and, I believe, neither most of Schemers do. The only thing I do have now is that it's not enought to be perfect language which can solve all problems in this world. Concurrency, networking, weak data, etc. These are not in the specification (maybe yet) but absolutely needed. If there's something lacking, then language specification should grow even if it's got bigger.
The world of computer is growing like speed of light. Problems to be solved are zillion. Too small wouldn't solve. We need small enough.