If gas prices go to $8/gal we might all be wearing tweed. If youre a designer or a famous and flamboyant writer, then tweed with a shawl lapel may be good.
Clothing is not something you can decree but elements of clothing have developed universal and in some cases local messages, especially for men. People dont expect tweed suits to have shawl lapels.
Style is something that you cannot teach, it has to be developed and it has to be an examination of what looks good for you and suits you. To look at something in a vacuum may not do one thing for your personal style. Which is why so many stylish people seem to do special things with conventional clothes. it worries me a little when someone they focusses on an extrinsic element to the detriment of their personal style growth.
I say this because the OP's question is important but not so much for its literal meaning as what should be the main thrust. Wearing a standard sports jacket as stylishly as you can. When that's achieved the wearer will answer their own question about shawl lapels.
And this is why I prefer to get people to think about clothes rather than hand them an off the rack answer. Teaching a man to fish vs. handing them one.
What's the message you want to send? Men generally dont get shawl lapels so they are distracting if you do. They are especially distracting on a sports jacket because you presumably already have a unique pattern.
I saw Bill Maher on his HBO show and I couldnt figure out what was wrong with his suit. I eventually realized he had some sort of extra thin lapel on a dark chalk stripe suit. I thought that was strange for someone who wanted to be taken seriously. Is he really a comedian doing a political show or is he a new breed of political commentator? He might even be confused. I couldnt get passed the skinny (I think shawl style) lapel even when i chalked it up to his being in entertainment.
Maybe he doesnt care. Clothes are unlike other items, they have multilayered meanings depending on whos wearing them and whos observing. If you are the straight and narrow, there are conventions to follow. We've been conditioned and if you break with convention you have to be confident.
For example, I love Duchamp ties (Amongst others), and theyre very English dandy. Some guy here who dresses like a beach bum and has poor personal hygiene thinks theyre crazy ties. Cant please everyone. i like the way they compliment what i wear, I know the sort of person they impress and he's not one of them.
Never say anything in 50 words when 500 are at the ready. Though what you are trying to say, as usual, escapes us all.