I think Cathay Pacific currently has agreements with Air China for eg. capability with Asia Miles also codesharing would allow OW's exposure to China.
Furthermore, since Cathay Pacific is an Hong Kong based airline, it would not be surprising to see China may offer all 5th to 8th traffic rights to all Hong Kong passenger and freight carriers as a part of CEPA hence Cathay Pacific can acutally operate in China hence no Chinese carriers is necessary.
For South East Asia Network, I think OW may need more exposure, but it can do it not even to invite a new airline to come in. JetStar Asia/Pacific, a Qantas Group Airline, is now a big profit-driver for Qantas Group. So OneWorld can try to liaise with Qantas to form a new full-service airline or to convert 3K/BL to full service with other OW Airlines - a joint venture project will help simply. This might work even better.
Finally for Brazilian network, I think LAN can try to set up LAN Brazil sometime later as of their other LAN Airlines. I don't think OW will need a new airline for that region tho.
The only region left over might be Central Asia, which would pretty despreate a new airline to join. But I believe 9W and IT knows their position in any alliance is so important hence they will rather not to join at this time until those 3 alliances offer enough prviliages/terms favourable enough for 9W & IT to join.