I don't think the dress code will change per se, at least not in the beginning. But if the new government manages to carry out the reforms of the House of Lords like it was announced in the King's speech none of the hereditary peers will have a seat in the House of Lords. Naturally their spouses will not attend the State Opening of Parliament either anymore and although some life peers would probably be able to buy their wifes a tiara, those old grand heirlooms belonging to the hereditary peers (the majority I would imagine) will be put back in the safe only to be brought out (if even then) in the event of a family wedding.