I am advising my client to embed “Diagram” artifacts inside a text based artifact just because of the limitation discussed here:
https://jazz.net/forum/questions/223497/unable-to-export-artifacts-of-format-diagram-from-rdng-601-using-custom-rrdg-template
However, these embedded artifacts are not exported using a custom RRDG/RPE template when you export the rich text content of the text based artifact.
Found that we have to use the parameter ( as per IBM support) '&maximiseEmbeds=true' to expose these embedded artifacts in REST API. Somethings like https://server:port/rm/publish/text?resourceURI=_429c13f5336a4b39b8f24342bcaa2ee7&maximiseEmbeds=true works fine if you are exporting it from RPE and only from a single artifact.

Consider a scenario in which I have to export 10 text artifacts which has embedded Diagram artifacts. In this case I have to use a URL like "https://server:9443/rm/publish/text?projectURI=_0M01kBxbEeavIZKujfEbTw" in the DocSpec ( from a stand alone RPE document generation tool). Here I cannot use the parameter  '&maximiseEmbeds=true'.

The only way I could do this is to use a "Data Source Configuration" element in RPE template and dynamical reconfigure text artifact URLS to https://server:port/rm/publish/text?resourceURI=_429c13f5336a4b39b8f24342bcaa2ee7&maximiseEmbeds=true  , so that RPE will be able to see the embedded artifacts and export it.

But you know, using "Data Source Configuration" element in RPE/RRDG template will take a hit on performance. So couple of questions:

1. How can I export this text artifact with embedded Diagrams without using a "Data Source Configuration" element in a custom RPE/RRDG template. May be we have some settings in RDNG 6.0.1 which can always show embedded artifacts without using the '&maximiseEmbeds=true' parameter. 

2. Just take a look at the in built (OOTB) 'reqspec' RRDG template (JazzTeamServer_6.0.1\server\conf\rm\reporting\initialization\templates\rrdg) which does not uses "Data Source Configuration" element. But still it can export those embedded diagram artifacts, if you select the check box "Show embedded artifacts maximized" in the RDNG export wizard. I can also see an external variable "showEmbedMaximized" used in this template but could not locate how it has been used. So what is the technique we have used in "reqspec" template which could export embedded diagram artifacts from a text artifact without using a “Data Source Configuration" element.

Best Regards
Abish M Zachariah