I don't think the 2008 crisis was caused by complexity. Most actors on these structured credit markets understood well the products. It was rather caused by over leverage and complacency toward credit risk.

And it will happen again. Hopefully the banking system is much stronger now, and the legal mechanisms are in place to limit the cost of a failing bank to tax payers. But the excess of liquidity as a result of money printing has starved investors for yield, and I believe that they are investing in places where they would rather not, like in 2005. Then it was subprime and commercial real estate. Now most likely emerging markets.