ICANN had commissioned a technical study from Bond Internet Systems SL to look at the impact of using DNAME resource records [RFC2672] in the root zone of the the Domain Name System (DNS).

The study concludes –

All the tests performed in this study indicate that the introduction of DNAME records as a means of creating isomorphic TLDs does not prevent name resolution using software in common use today.

The observed behaviour of DNS servers varies in the handling of the DNAME record and the caching properties of the synthesised CNAMEs but this does not affect the outcome of the resolution process.

Differences in caching behaviour may generate different load profiles in the DNS servers but do not prevent resolution completion.

Finally, while hard to quantify without well known query patterns for the potential new TLDs (popularity, etc) the introduction of DNAME in the root zone is highly unlikely to generate any significant impact in the load of root servers.

ICANN Announcement here