Hi Flo. I'm gonna pick sides with 'Not Advisable'.
Two reasons:
1) This is a fiduciarily irresponsible decision. Translation: That's an expensive path to commit to. You're throwing out all the money CA & others have committed to what's already been matured in the tool and committing to building it all yourself. There are hundreds if not millions of dollars of functionality (Demand Management & CRM views, Reports & Portfolios, etc) built around Ideas. If you choose to 'go it alone' and create a new object - you throw all of this out. It's worth the effort to weigh the pros and cons of this. Example:Clarity 13.2's OOTB Portfolio Management feature. Would the organization benefit from seeing the Demand in Ideas stacked in with the 'committed' work in Projects and evaluate what to work on through what if analysis? Clarity 13.2's Portfolio Management features do this. If you choose to forgo the Idea object - you lose all this good work. Same goes with other reports, portlets, processes, etc. If you go it alone - you're alone. You've committed to building it all yourself and this is expensive. Isn't not building a PPM system yourself why you bought a COTS system?
2) This too shall pass. When we got off the ground with Clarity, an executive leader asked to scrub the word & all functionality around Approved from the system. "We're a cost center funded by our customers! We don't approve anything! We're purposely funded to do this work!" Technically... not incorrect, but a little hung up on semantics. Welcome to the coaching moment. Ask people to remain curious and take the long view. We now use 'Approved' as a very important state in the system and have new functionality upcoming that will make this even more important (Much out of the box functionality does too.). I'm glad we sat in the pocket and took the hits on this one. Take the time to try to understand the value in a feature and trust that it's probably been thoroughly 'field tested'. When questions arise, use forums like this for answers or to bounce ideas (like you just have!).
The Process: OK - the above is subjective opinion. Now let's look at the objective process you will kick off.
1) List your requirements.
2) List the pros and cons of each (classic 'build vs buy') and be prepared to put dollar values with them.
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Stay Curious! - Run the above process.
I've networked with institutions that have custom Portfolio Management objects that integrate with their other enterprise systems that do *exactly* what they need. The OOBT Portfolio Management features don't provide them value - this is OK. 'Pros' land on 'Custom' for them on this.
We do not use CA's Status Report sub object & surrounding COTS stuff. We were off the ground before theirs came into being and have greater functionality. This we value ($$). 'Pros' land on 'Custom' for us on this.
You may find your new, custom 'Idea' is right for you. All I ask is be prudent, take a fudiciarily responsible long view and base the decision on a fully vetted bake off.
This has been successful for us. Hope it helps you as well.