I like the idea of a starting guardsman unit to prevent rushes. You could have a long term upgrade tree with it (free upgrades of course) to keep it relevant throughout the game.
Now I will explain my idea. I would say that LM terrain would be the best approach, as you could still retain the normal sea squares everywhere else with their normal one movement cost (it has to be one, because the newer ships will not ignore their cost, because if they did they would not be able to use the lanes). The sea lanes would replace the Atlantic wall (if you look in the editor, it is the long line of sea squares down the Atlantic.
A new line would have to be put through the Indian Ocean, and would end in Micronesia. A line would also have to be put going toward the bottom tip of South America, leading up to the Hawaiian islands (which have been a crucial stop for ships since coal crossings of the pacific started). This line would terminate near Japan and China.
Another line would have to be extended to the... Persian Gulf (I think, not 100%)... basically the body of water which would be connected to the Suez canal. That water should also probably be Sea Lane water as well, and there should be some sea lane water near the Panama Canal as well... although these areas will not be NEARLY as crucial if this change is made *they should speed you up a bit, as it will not be possible to connect those lanes under the Horn of Africa and the Southern end of South America*. Which makes sense, considering the storms those areas suffer.
The Atlantic line would need to be totally connected, as it currently has ocean gaps, and a Transverse line may need to be added to allow easy movement from Europe to America and VV.
There are several important reasons for this change:
1) I am tired of spending a century doing as England what Russia was able to do in the real world in under a year in the Russo-Japanese war; send ships from Northern Europe to the Tsushima Straights for a war! Although, unlike Russia, I do not intend to lose.
2) In a game where it is possible to railroad from Lisbon to Peking an infinite number of times in a single turn, it should not take an entire game to do the same thing with a boat.
3) COLONIAL WARFARE
It is simply impossible for the Euros to settle the Indies before the Middle Easterners and the Easterners do it. While they would get the same advantages (although I think they should get them a bit later, simply to allow the Euros to do their colonial thing), the Europeans would be more likely to capitalize on them. Besides, it makes it possible to invade those areas with the (most likely) superior tech of the european superpower without having it take so long that the units are outdated before they arrive.
4) Naval Combat:
People would be forced to keep an eye on those lanes. Think how vicious the computer will be with them; China could declare war on you and ACTUALLY DO SOMETHING to you, even if you ARE in Europe. And, even cooler, VV. How cool would it be to see China fighting a war against Europe to preserve its independence, and seeing the troops from Europe not trekking across the vast Russian steppes, but sailing there on nice new boats!
5) Because I'm Rick James, biatch! ;p
6) Boosting the movements of ships will cause you to have severe problems with long range invasions from hell that can transport units multiple times. The beauty of this solution is that you will not have to increase movement; you may even have to reduce it for late middle and onward to compensate for their massive sea lane advantage!
7) The computer will actually use this! They cannot help it, as they compute based on minimum move cost, and sea lanes would certainly equal the absolute minimum... so you could stick ships near there with reasonable certainty that the enemy WILL actually show up around there... as opposed to simply setting up destroyers all around your coast.
If you bothered to read this, you have as little to do as I do... which is probably why you are on this site in the first place ;p
I think, repeat THINK, that this change would be a very useful one, in that it will reduce transit times for boats in an accurate fashion, without requiring inordinately large numbers of movement points for each boat, and the subsequent rebalancing that this would entail, as there would be no way to intercept them before they reached a coast.
Rhye, if you want me to clarify something in specific, just ask; I am simply making as strong (if wordy and somewhat incoherent) case for my idea.
LONG LIVE THE SEALANES! ;p
The Merkava is probably one of the best defensive MBT's in the world. Unfortunately it is also one of the slowest and heaviest. So this is probably the only tank fast desert movement shouldn't apply to! 
