1. Cross collateralisation reduces the amount of funds a borrower can qualify to borrow,
2. It then also reduces the number of investment
properties a borrower can buy
Whilst I agree with the sentiment, and they certainly are risks associated with x-coll, technically speaking this isn't true.
X-coll neither reduces nor increases how much you can borrow, nor does it change the number of investment properties you can buy. What it does is it takes away your flexibilty to move and choose different lenders.
Your borrowing capacity should be the same with the CBA regardless of if your portfolio is crossed or not. Crossing only means you can't easily move to the NAB when the CBA won't lend you any more.