First of all, it's important to understand that if you are running Zabbix 2.4, you will lose support from Zabbix as 2.4 is not a long term release such as 2.2. So, it's probably wise to upgrade.

The 2.x series will come to an end, there will be no Zabbix 2.6 coming out, and Zabbix will move on to version 3.0.

So what can we expect from Zabbix version 3.0? So far, it seems that Zabbix 3.0 will continue for focus on improvements. A full overview of what is already added can be found on the Zabbix webpage:

http://www.zabbix.org/wiki/Docs/roadmap

In 3.0, a major improvement will be full encryption between Zabbix server, clients, and proxies.

SNMP discovery has been improved to support the low-level discovery of multiple OIDs.

Finally, no more dropdown menu for mass editing, enable, disable, and delete. Instead we now have real buttons.

The API has been partially moved to the server side: http://www.zabbix.org/wiki/Docs/specs/ZBXNEXT-2519#Move_API_to_Zabbix_Server.

Many other improvements are being made for Zabbix 3.0. A full list of what's new can be found here:

https://www.zabbix.com/documentation/3.0/manual/introduction/whatsnew300

I think that we can expect in the upcoming 3.x releases some interesting improvements, but I will not make any predictions here. To get a good idea what Zabbix will try to improve or add, I suggest you watch Alexei's latest presentation from the Zabbix conference where he points out a few shortcomings and annoyances of Zabbix that he wants to improve over the coming years: https://www.youtube.com/watch?v=SwuqNIJIb_o.