Encontrei a resposta: Sim, isso é proibido pela política da ICANN
The SSAC stated that dotless domains would not be universally reachable and recommended strongly against their use. As a result, the SSAC recommended that the use of DNS resource records such as A, AAAA, and MX in the apex of a Top-Level Domain (TLD) should be contractually prohibited where appropriate, and strongly discouraged in all cases.