Building an expansion for an A1200 which could rival even the bottom of the range Sam 440ep would not only cost a lot more than the Sam, but would also have to basically use the A1200 as a glorified keyboard and mouse adaptor. The rest of the system is just too slow.
Remember, if Phase 5 were charging £500 and were making PPC cards in the thousands, why would a new card with a tenth the market cost any less?
Trust me, new PPC cards are not going to happen. It makes zero sense both technologically and financially. 68030 cards, on the other hand are a different ball game entirely...