But seriously, it's necessary to consider the cost tradeoffs of including sophisticated software within SONAR. The whole point of plug-ins was so you could customize a "stock" setup to fit your needs, and thus avoid having to shell out money on features (plug-ins, instruments) for which you had no need.
Ultimately I think we're talking about three possibilities here.
1 For hardcore mastering, you would invest in a fully-featured program like Wavelab or invest in plug-ins like Ozone because it would be cost-prohibitive to build those features into SONAR.
2 For typical, less-critical mastering projects, SONAR could be enhanced to handle them without causing a price increase.
3 There could be a "SONAR Ultimate" version for $999 that integrated mastering tools but would still cost less compared to buying SONAR and a suite of mastering plug-ins.
Of these, I think 2 would provide a significant benefit to a large number of SONAR users. Then we can dream about 3