SYD-LHR would usually be booked as a single segment on either BA (as BA 16) or on QF (as QF 1), even though in either case it is a single direct flight comprising two legs.

If there is a list of multileg flights, I do not know of it.

If you mean is there a list of two-segment flights equivalent to a single segment flight (like BA 16 SYDSIN, followed by BA 12 SINLHR is very similar to BA 16 SINLHR with a stop in SIN), I would doubt this exists.

However if you have some specific journey in mind, I am sure the collective wisdom here will be able to answer your question. :)

So - might KTM-xDOH-JNB be an option for you?

Good idea, I'll look into it.

So, here's something weird. I had my itinerary continuing from AUS to LAX-HKG-JNB-DOH. I called the RTW desk to change it to AUS-LAX-JFK-MIA-YUL-DFW-HKG-JNB-DOH. They quoted me additional $400 in taxes and I'm just trying to understand how that's possible since I've basically added mostly domestic sectors. And both old LAX-HKG and new DFW-HKG are on AA metal. Any ideas?

Okay, just called RTW desk again and they're saying it's because of the Canadian "immigration taxes" on the MIA-YUL-DFW segments. I've never seen those that high before.

ITA shows the following +++ for a MIA-YUL-DFW routing on AA (with 36 hours in YUL):US Transportation Tax (US)
$45.75

US September 11th Security Fee (AY)
$5.60

US Passenger Facility Charge (XF)
$4.50

US Flight Segment Tax (ZP)
$8.20

Canadian Air Travelers Security Charge (CA)
$10.00

Quebec Sales Tax (XQ)
$2.00

Canadian Goods and Services Tax (XG)
$1.00

Montreal Trudeau Airport Improvement Fee (SQ)
$19.70

US Customs Fee (YC)
$5.50

US Immigration Fee (XY)
$7.00

USDA APHIS Fee (XA)
$3.96
That's a total of $113.21.

That's what I saw on ITA as well, but I'm not sure how to convey this to them..

Ask them to give you a breakdown of additional taxes that need to be collected, versus paid (PD), in the two-letter tax codes. Compare it with the breakdown above.

D Inventory for OneWorld Explorer - Online Tool vs Expertflyer Differs
 

I am currently trying to book a DONEX itinerary for departure in just a couple of days ex Tokyo. I have been using the oneworld online booking tool but have noticed that for several flights on JL (ORD-Tokyo) and CX (EWR-HKG) the tool shows no availability while expertflyer has multiple D seats available. Is there a reason for this, and would calling carriers directly show more availability? Thanks so much for any perspective that could be provided.

About to ticket a DONE3 with base fare 6,200 USD out of the port famous for 'very strict security', is it the best that one can do nowadays?

(Not sure if it should be named in case it gets shut down or something.)

Any experiences with security questioning/interrogating with having a RTW itinerary (and touching some ports that they might find offensive?)

Either a bug or a POS (Point Of Sale) issue.

I am seeing DONE3 ex-TYO for 5,898 USD. If this is easier for you to position you might want to consider this to save you (loads of) hassles.

I just re-routed a MPM DONE5 that was ticketed on Aug 1 2016. The PNR code changed, is it normal that one gets a new PNR for rerouting?

It has never happened to me, and I fly at least one DONEx per year, and have done so for many years.

i find it very strange... i wonder why...
but the fare information is intact, at least from the receipt.