I think IG management have got it wrong unless the fall in profits are due to increased membership placing small trades.
I would very much doubt cost of maintaining membership in this electronic age where IT systems scale up and down very easily, is the cause of fall in profits... Moreover, IT costs are more likely to be fixed for circuit lines and data feeds. Doubt they pay a license fee for every user.
Big question, is the marginal cost of extra membership greater than the marginal return from each player? I doubt it somehow.
How will changing the composition of traders increase profits? Will the bigger players suddenly start placing more bets/trades or bigger sizes?
One plausible idea that comes to mind; if they purge the bottom 25% of their traders and cut staffing & costs by a similar or greater 35% making the business more productive and focused on brokerage fees perhaps???
What message does this send out to aspiring traders? You are not worthy of our attention, run along somewhere else who will take your coins...
Alternatively, will IG attract bigger players from other SB companies?
Can Amazon increase sales by placing a restrictions on ordering minimum of 2 3 or 4 books or minimum purchase price by not selling anything under £5.
In general I think it is not a good change. Time will tell...