Rumors stemming from an Australian publication point to the new Mazda MX-5 Miata platform as a basis for the next generation Scion (Toyota) FR-S and Subaru BRZ. Although this could fizzle out and turn out to be complete nonsense, there is some logic to the idea. After all, Toyota is the common denominator. Toyota owns Scion as a brand, is a major shareholder in Subaru and shares manufacturing space with Subaru, and recently Mazda and Toyota announced that they would be working closely together going forward.
Consolidation of platforms is widespread in the auto industry. VW, Toyota, GM, and every other major automaker have all moved to reduce the number of platforms from which they spawn multiple models. It is no secret that many Audis and VWs share almost all their important, expensive parts. Nor is it any secret that a Chevy Tahoe and Yukon Denali are the same vehicles barely changed for buyer preferences. The general idea is to make as many of the pricey parts as possible and then style the vehicles to meet a brand identity.
Automakers are well past the point now where consumers care about platform sharing. Even two cars as similar as the Scion FR-S and BRZ can be marketed to different enthusiast groups. If Toyota chose to, it could use the Mazda MX-5 platform and create a coupe or sports convertible easily, just as Fiat has already done with its 124 Spider.