I am fairly new to the noSQL world, and although I understand the benefits of performance and "cloud" friendliness, it seems the RDBMS world is much simpler and standard and limited to fewer players

I worked with SQL Server, Oracle, DB2, Sybase, Terradata, MySQL and others, and it seems they have in common much more (in terms of Query language, Indexing, ACID, etc) than the noSQL family.

My question is mainly this

1. Is it at all a valid concept to move an existing Spring/Java EE+JPA app to a noSQL storage? or it will require a complete re-architecture of the system beyond the medium of storage?
2. Hoping it's a valid goal, are there any migration paths that were case studied as best practices?
3. Is there an equivalent to the concept in "noSQL" that is comparable to ORM for RDBMS? e.g. any layer of separating the storage implementation from concept (I know GAE BigTable supports JDO and JPA but only partially, is there a newer JSR for a more noSQL friendly JPA?)
4. Are there any attempts to standardize "noSQL" the same way RDBMS are (query language, 
API)
5. Is "noSQL" a too wide term? Should I modify the question per implementation (KV/Document)