On limited space

There doesn't look to be much too controversial about the decision to build a glass-topped temporary home for the House of Commons. But one aspect of the plan seems rather odd given the problems with the current chamber:

The temporary Commons chamber will have exactly the same dimensions and layout as the existing one, complete with tiered seating for MPs and overhanging visitors’ galleries.

So what could be the problem with matching the current dimensions?

The House of Commons chamber can physically hold only 308 seats similar to the desk-and-chair combination now used. After the 1997 riding redistribution left the House with 301 MPs, it was renovated to hold 304 chairs for sitting members. That number jumped to 308 with the round of changes that took effect with the vote on June 28, 2004. Before that election, the Speaker's Office told CBC.ca that four more chairs and desks had been added in the room's northeast corner, to the Speaker's left, replacing a sitting area for the parliamentary pages. Now there's no more room for expansion.

However, riding redistribution must by law take place every 10 years, adjusting the federal electoral districts to reflect population changes. All provinces are guaranteed that their number of federal seats will not decrease, even if their proportion of the Canadian population shrinks dramatically. So the number of seats is bound to keep going up in the absence of dramatic changes to the way we elect a government (through bringing in some form of proportional representation, for example).

So is there some reason why the temporary chamber is being matched to the current, insufficient amount of space, rather than leaving more room for expected growth in the number of MPs?