Yes. Processes natively talk to each other.
But such a platform needs to be deeply architected for modularity of UI, agility of process model and coherence of the data model.
And it absolutely needs a unifying vision beyond that: style, execution, patterns, seed models, standards etc - they all come into play.
It also requires a focused development model that is specific to process-driven architectures.
Yes, ONE business platform can orchestrate your business completely. Connecting line-of-business applications with a process layer to utilize best all systems of record, ONE business platform - with solid integration capabilities - can handle ALL business processes. Depending on gathered requirements and agile delivery methodology, it can also do it rapidly and scale fast after the first processes by reusing centain artifacts and components.
That typically depends on what you intent to do... If you want to map all your processes on a high enough business level (as in understandable), you could map all of them in (bias here) Elements.cloud say. However, if you want only to create executable BPMN flows in order to automate (parts) of your business processes you would need something else (e.g., Signavio). Bottomline, I suppose you need an umbrella type of "this gives us insight and oversight at a business level, to be used for Lean exercises)" solution and add more techie stuff that would sit in context of that umbrella solution. Most of the time, organisations lack the umbrella (or have a poor, hard to manage Sharepoint type solution... or even worse, a collection of outdated Visio's, Powerpoints or Word docs...).
I know our DBPlatform can handle all required business processes. As I have explained before we established that relatively few task types can compose any operational business process. We even have proven build of an Intelligent process which can recognise past actions to bring forward the optimal outcome. It can readily build configurators with in built rules and automatically delivers the adaptive capability all achieved with a no/low code platform. We have been ridiculed and ignored as we were decades ahead of the game. But the technology which is well proven with early adopters has survived against the odds. As they say watch this space..
..just a question of time......and the "game" will change.....at great cost to some rather large vendors and their ecosystems.
I consider this question as asking for requirements – what are essential capabilities of a business platform to handle all types of business processes.
Just a small addition to Bogdan’s list – such a business platform must be able to compete with blockchain-based smart contracts.