I've discussed this with the biblatex maintainer and we will probably aim for a style implementation of this with biblatex 3.x. With 1.7/0.9.6, the following will be possible. You will have to use the experimental biblatexml datasource format for such entries (you can still have all of your normal entries in bibtex format).
<?xml version="1.0" encoding="UTF-8"?>
<bib:entry id="yanagida_zengaku_sosho_1975" entrytype="collection">
<bib:title mode="romanised">Chūbun shuppansha</bib:title>
<bib:title mode="translated" xml:lang="en">Collected Materials for the Study of Zen</bib:title>
<bib:location mode="translated" xml:lang="en">Kyoto</bib:location>
<bib:publisher mode="romanised">Chūbun shuppansha</bib:publisher>
There is no way to do this with bibtex format but this is no problem for biber - you can have many datasources of different formats. With the above example, you could choose to use the display format "romanised" and biber would construct the .bbl with only the romanised mode fields, for example. There will be no way to use mixed modes in the same entry however as this would need a radically enhanced .bbl format and massive internal biblatex changes which are planned for version 3.x
The above example uses the global displaymode setting (which will be in biblatex 1.7). You will also be able to set per-entry modes with an attribute on the entry, for example:
<bib:entry id="yanagida_zengaku_sosho_1975" entrytype="collection" mode="translated">
The default mode is "original" which matches fields with no mode specified too.
Edit on release of biber 0.9.6/biblatex 1.7: This is now implemented as mentioned. The default global setting is:
this biblatex macro is undocumented at the moment but you should be able to use it to change the global displaymode choice order. You can also set displaymode per-entry as shown above. Let me know on the biber SourceForge forum if you have problems.