According to my understanding latest features are available in apache cassandra instead of Datastax enterprise.

First they are implemented in apache cassandra which datastax incorporates in DSE.

Like cassandra version 3.0 is incorporated in DSE 5.0 which released few days back (21st june 2016), the same version of apache cassandra will be supported till May 2017.

Also as far as other integration are concerned spark integration is very much possible using spark-cassandra connector thanks to datastax.

There are also some open source cassandra lucene indexer available, which you can use.

Yes Datastax was providing opsCenter free to use till verion 5.0; Opscenter 6.0 is available in DSE only.

EDIT:

Graph integration is based on Titan dB which datastax bought. So Apache Cassandra doesn't have that capability. Solr integration can be achieved using open source version like solrandra. Though Datastax has provided spark Cassandra connector. Datastax has contributed the community in form of drivers and let's hope datastax keeps on contributing to the community. And Apache Cassandra is pretty good to achieve most of the functionality.

Also datastax is providing DSE for free to start-ups . Refer Datastax startup pprogram.