Thanks a lot for supporting ECDSA certificates! Now I can use authenticated ciphers (AES_GCM) on IIS (WinSvr2012R2) and on the IE11 clients on Win7/8.1.
For my own sites, I took the opportunity of using a ECDSA certificate to disable TLS 1.0 and 1.1 and all non-AEAD ciphers like AES_CBC (as, according to Adam Langley, "everything less than TLS 1.2 with an AEAD cipher suite is cryptographically broken’). This means some older clients cannot connect to it (e.g. Safari on OSX 10.10), however IE11 on Win7 can connect, so this is OK for me.
Because browsers like Firefox and Chrome don’t use AES256_GCM (as the security benefits of AES256 are not to be worth the performance tradeoff, as stated on a chromium bug entry) and a P-256 ECC key only provides ~128 bit symmtric key strength, I also disabled AES256, and because Chacha20_Poly1305 is not yet supported on SChannel, TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 remains as the only available cipher. 
Here is the Ssllabs report for one of my sites. 