Dashboard UI Expression has a limit of 2000 characters - can this be increased.

No, it can't be increased. We recommend putting complex dashboard UI expressions in rules: forum.appian.com/.../Record_Design

I've been trying that:
Expression Rule:
='type!{www.appian.com/.../2009}ListViewItem'(
title: ri!incidentHdr.ServiceType&" #"&ri!incidentHdr.CaseId,
details: ri!incidentHdr.CaseTitle,
timestamp: ri!startTime
)

List View Template:
=rule!createRecordHdr(rf!incidentHdr.ServiceType, rf!incidentHdr.CaseId,rf!incidentHdr.CaseTitle, rf!pp.startTime )

But this isn't working, any obvious errors?

Ok, ignore me. It's late here in the UK and I'm struggling to copy and paste apparently. Got it working now. Thanks!

For the first parameter you are passing the value of rf!incidentHdr.ServiceType into the rule input that I assume is named incidentHdr and are then trying to access the ServiceType field of that input.

So it's like doing incidentHdr.ServiceType.ServiceType.

Give this a try:

Expression Rule:
='type!{www.appian.com/.../2009}ListViewItem'(
title: ri!serviceType&" #"&ri!caseId,
details: ri!caseTitle,
timestamp: ri!startTime
)

List View Template:
=rule!createRecordHdr(rf!incidentHdr.ServiceType, rf!incidentHdr.CaseId,rf!incidentHdr.CaseTitle, rf!pp.startTime )